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  • richardmitnick 7:00 am on June 15, 2017 Permalink | Reply
    Tags: , , , , Clouds over the sunlit arch, , Hot Jupiters, WASP-12 b   

    From astrobites: “Clouds over the sunlit arch” 

    Astrobites bloc

    Astrobites

    Jun 15, 2017
    Eckhart Spalding

    Title: High-temperature condensate clouds in super-hot Jupiter atmospheres
    Authors: H.R. Wakeford, C. Visscher, N.K. Lewis, T. Kataria, M.S. Marley, J.J. Fortney, A.M. Mandell
    First Author’s Institution: Planetary Systems Lab, NASA Goddard Space Flight Center

    Status: Published in MNRAS [open access]

    Introduction

    Having grown up on Earth, we tend to associate cloudy skies with brisk weather. Even gloomy weather. As Robert Frost said, if it’s the month of May and a “cloud comes over the sunlit arch” you’ll find yourself “two months back in the middle of March”. How different are clouds on alien worlds? Is there such a thing as searingly hot clouds, suspended high above in skies so bright they make your eyes ache when you shut them tight?

    If we want to study alien clouds outside our own solar system, “hot Jupiter” planets are our best test subjects. Hot Jupiters are gas giant planets which orbit very close to their host stars. Their atmospheres are relatively easy to characterize if they pass directly in front of their host star [transit], which allows light from the host star to pass through their extended atmospheres and provide us with transmission spectra.

    Planet transit. NASA/Ames

    In this light (no pun intended), the physics of clouds have experienced a recent surge of interest in the exoplanet field. Clouds play critical roles in an atmosphere’s energy balance: they can reflect light back into space, trap heat, remove absorbing compounds, influence wind structure and chemical reaction times, and exert feedback effects on atmospheric temperature-pressure profiles. Clouds also complicate measurements of chemical abundances, because clouds tend to dampen absorption features and can transmit photons as an unknown function of wavelength. (Remember when you got sunburned on a cloudy day?)

    Clouds in exoplanet atmospheres are a little bit like turbulence or magnetic fields in star formation– they add a rich level of physics to what would otherwise be a much simpler physical picture. But the first strong evidence of thick cloud decks on exoplanets dates only from 2014, and we still don’t know much about the nature of those clouds. (In fact we’re still working on Earth clouds. Earth is, after all, a little-known planet.)

    Today’s paper

    The authors of today’s paper push the boundaries of knowledge into the most scalding area of parameter space: the realm of sizzling “super-hot” Jupiters, with temperatures of more than 1800 K. Part of the authors’ motivation is to address a longstanding puzzle. The temperature in most planetary atmospheres should become colder at higher altitudes. But according to models, hot Jupiters with very high incident flux levels are expected to harbor high-altitude atmospheric absorbers like TiO or VO. If these compounds are present, they will cause a “temperature inversion” where temperature actually rises with altitude. Strangely, however, these compounds or temperature inversions have been difficult to find in hot Jupiters.

    2
    Fig. 1: The transmission spectrum of WASP-12 b. The y-axis represents the effective “thickness” of the atmosphere at a certain wavelength. Actual data are in the form of black data points, and pure condensate curves are in orange and green. The relative flatness on the left side of the plot indicates the presence of clouds. Before the James Webb Space Telescope (JWST) fills in the right side of this plot, the condensate models cannot be well distinguished. (Fig. 5 from today’s paper.)

    NASA/ESA/CSA Webb Telescope annotated

    The authors begin by considering the hottest condensates that may exist in a hot Jupiter atmosphere: calcium (Ca), titanium (Ti), and aluminum (Al). They assume cloud formation occurs when rising air reaches vapor pressure saturation, and that clouds stop forming when one of the constituent elements is depleted. They calculate the resulting relative cloud masses, play around with the atmospheric metallicities, and overlay temperature-pressure curves on condensation curves to see what types of clouds should form. Among their findings, Al compounds will form much more cloud material than Ti, and higher atmospheric metallicity levels allow the formation of more massive clouds.

    The authors turn to the specific case of the planet WASP-12 b. The transmission spectrum of WASP-12 b exhibits some water absorption but is otherwise fairly flat, which indicates the presence of clouds.

    3
    Fig. 2: Left: Solid colored lines represent temperature-pressure curves in different regions of WASP-12 b.

    4
    Hubble Finds a Star Eating a Planet. Artist’s concept of the exoplanet WASP-12b. Credit: NASA/ESA/G. Bacon

    NASA/ESA Hubble Telescope

    Dashed lines represent condensation curves for different compounds. Clouds will form between the temperature-pressure and condensation curves. For example, iron (Fe) clouds will exist on the night side at altitudes corresponding to pressures in bars (P) below log(P) = -1.5. Pressures accessible to transmission spectroscopy are between about log(P) of -1 to -4. (Note that pressure decreases as the y-axis increases.) Right: An alternative representation showing the effect of distance from the substellar point. Clouds will form on the nightside side of the lines. Vertical dashed lines show the regions between day and night sides probed by transmission spectroscopy. (Fig. 4 from today’s paper.)

    After doing some more model calculations, the authors overlay condensation curves on a 2D plot of temperature as a function of pressure and longitude. Interestingly, the clouds roasting in WASP-12 b’s atmosphere start to form right around the regions accessible to transit spectroscopy. At temperatures of less than 1900 K, WASP-12 b’s clouds can shroud the signatures of TiO or “hide” its constituents via condensation.

    There still is much work to be done in understanding clouds among the worlds that “favor fire“. Condensation nuclei and condensate growth are very poorly constrained, and more lab work is needed to determine the optics of different compounds. But there is light on the horizon (again no pun intended). Certain absorption bands including Ti-O vibrations are within the discovery space of JWST, which may allow us to distinguish between WASP 12 b clouds which hide TiO or remove Ti from the gas phase.

    That would bring us full circle: after predicting the compositions of clouds on super-hot Jupiters, today’s paper has left us with a test observation to disentangle the effect of clouds on WASP-12 b. That test will get us another step towards resolving the mystery of the missing thermal inversions.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 6:01 pm on June 5, 2017 Permalink | Reply
    Tags: , , , , , HAT-P-38 b, Hot Jupiters, , WASP-67 b   

    From Hubble: “Hubble’s Tale of Two Exoplanets: Nature vs. Nurture” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    1
    Release type: American Astronomical Society Meeting

    Atmospheres of Two Hot Jupiters: Cloudy and Clear

    Astronomers once thought that the family of planets that orbit our sun were typical of what would eventually be found around other stars: a grouping of small rocky planets like Earth huddled close to their parent star, and an outer family of monstrous gaseous planets like Jupiter and Saturn.

    But ever since the discovery of the first planet around another star (or exoplanet) the universe looks a bit more complicated — if not downright capricious. There is an entire class of exoplanets called “hot Jupiters.” They formed like Jupiter did, in the frigid outer reaches of their planetary system, but then changed Zip code! They migrated inward to be so close to their star that temperatures are well over 1,000 degrees Fahrenheit.

    Astronomers would like to understand the weather on these hot Jupiters and must tease out atmospheric conditions by analyzing how starlight filters through a planet’s atmosphere. If the spectral fingerprint of water can be found, then astronomers conclude the planet must have relatively clear skies that lets them see deep into the atmosphere. If the spectrum doesn’t have any such telltale fingerprints, then the planet is bland-looking with a high cloud deck.

    Knowing the atmospheres on these distant worlds yields clues to how they formed and evolved around their parent star. In a unique experiment, astronomers aimed the Hubble Space Telescope at two “cousin” hot Jupiters that are similar in several respects. However, the researchers were surprised to learn that one planet is very cloudy, and the other has clear skies.

    The Full Story
    Ann Jenkins
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4488
    jenkins@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Giovanni Bruno
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-6823
    gbruno@stsci.edu

    2

    Is it a case of nature versus nurture when it comes to two “cousin” exoplanets? In a unique experiment, scientists used NASA’s Hubble Space Telescope to study two “hot Jupiter” exoplanets. Because these planets are virtually the same size and temperature, and orbit around nearly identical stars at the same distance, the team hypothesized that their atmospheres should be alike. What they found surprised them.

    Lead researcher Giovanni Bruno of the Space Telescope Science Institute in Baltimore, Maryland, explained, “What we’re seeing in looking at the two atmospheres is that they’re not the same. One planet—WASP-67 b—is cloudier than the other—HAT-P-38 b. We don’t see what we’re expecting, and we need to understand why we find this difference.”

    The team used Hubble’s Wide Field Camera 3 to look at the planets’ spectral fingerprints, which measure chemical composition.

    NASA/ESA Hubble WFC3

    “The effect that clouds have on the spectral signature of water allows us to measure the amount of clouds in the atmosphere,” Bruno said. “More clouds mean that the water feature is reduced.” The teams found that for WASP-67 b there are more clouds at the altitudes probed by these measurements.

    “This tells us that there had to be something in their past that is changing the way these planets look,” said Bruno.

    Today the planets whirl around their yellow dwarf stars once every 4.5 Earth days, tightly orbiting their stars closer than Mercury orbits our sun. But in the past, the planets probably migrated inward toward the star from the locations where they formed.

    Perhaps one planet formed differently than the other, under a different set of circumstances. “You can say it’s nature versus nurture,” explains co-investigator Kevin Stevenson. “Right now, they appear to have the same physical properties. So, if their measured composition is defined by their current state, then it should be the same for both planets. But that’s not the case. Instead, it looks like their formation histories could be playing an important role.”

    The clouds on these hot, Jupiter-like gas giants are nothing like those on Earth. Instead, they are probably alkali clouds, composed of molecules such as sodium sulfide and potassium chloride. The average temperature on each planet is more than 1,300 degrees Fahrenheit.

    The exoplanets are tidally locked, with the same side always facing the parent star. This means they have a very hot day-side and a cooler night-side. Instead of sporting multiple cloud bands like Jupiter does, each probably has just one broad equatorial band that slowly moves the heat around from the day-side to the night-side.

    The team is just beginning to learn what factors are important in making some exoplanets cloudy and some clear. To better understand what the planets’ pasts may have been, scientists will need future observations with Hubble and the soon-to-be-launched James Webb Space Telescope.

    The team’s results were presented on June 5 at the 230th meeting of the American Astronomical Society in Austin, Texas.

    The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.
    Credits

    Illustration: NASA, ESA, and Z. Levy (STScI)
    Science: NASA, ESA, and G. Bruno (STScI)

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 12:36 pm on April 18, 2017 Permalink | Reply
    Tags: , , Hot Jupiters   

    From AAS NOVA: “Samples and Statistics: Distinguishing Populations of Hot Jupiters in a Growing Dataset” 

    AASNOVA

    American Astronomical Society

    astrobites

    18 April 2017
    Jamila Pegues

    Title: Evidence for Two Hot Jupiter Formation Paths
    Authors: Benjamin E. Nelson, Eric B. Ford, and Frederic A. Rasio
    First Author’s Institution: Northwestern University

    Status: Submitted to AJ, open access

    5
    Figure 1: A gorgeous artist’s impression of a hot Jupiter orbiting around its host star. [ESO/L. Calçada]

    Frolicking Through Fields of Data

    The future of astronomy observations seems as bright as the night sky … and just as crowded! Over the next decade, several truly powerful telescopes are set to launch (read about a good number of them here and also here).

    1
    NASA/TESS

    Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile

    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile


    LSST Camera, built at SLAC



    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    NASA/ESA/CSA Webb Telescope annotated

    NASA/WFIRST

    FAST radio telescope, now operating, located in the Dawodang depression in Pingtang county Guizhou Province, South China

    That means we’re going to have a LOT of data on everything from black holes to galaxies, and beyond — and that’s in addition to the huge fields of data from the past decade that we’re already frolicking through now. It’s certainly far more data than any one astronomer (or even a group of astronomers) wants to analyze one-by-one; that’s why these days, astronomers turn more and more to the power of astrostatistics to characterize their data.

    The authors of today’s astrobite had that goal in mind. They explored a widely-applicable, data-driven statistical method for distinguishing different populations in a sample of data. In a sentence, they took a large sample of hot Jupiters and used this technique to try and separate out different populations of hot Jupiters — based on how the planets were formed — within their sample. Let’s break down exactly what they did, and how they did it, in the next few sections!

    Hot Jupiters Are Pretty Cool

    First question: what’s a hot Jupiter, anyway?

    They’re actually surprisingly well-named: essentially, they are gas-giant planets like Jupiter, but are much, much hotter. (Read all about them in previous astrobites, like this one and this other one!) Hot Jupiters orbit perilously close to their host stars — closer even than Mercury does in our own Solar System, for example. But it seems they don’t start out there. It’s more likely that these hot Jupiters formed out at several AU from their host stars, and then migrated inward into the much closer orbits from there.

    As to why hot Jupiters migrate inward … well, it’s still unclear. Today’s authors focused on two migration pathways that could lead to two distinct populations of hot Jupiters in their sample. These migration theories, as well as what the minimum allowed distance to the host star (the famous Roche separation distance, aRoche) would be in each case, are as follows:

    Disk migration: hot Jupiters interact with their surrounding protoplanetary disk, and these interactions push their orbits inward. In this context, aRoche corresponds to the minimum distance that a hot Jupiter could orbit before its host star either (1) stripped away all of the planet’s gas or (2) ripped the planet apart.
    Eccentric migration: hot Jupiters start out on very eccentric (as in, more elliptical than circular) orbits, and eventually their orbits morph into circular orbits of distance 2aRoche. In this context, aRoche refers to the minimum distance that a hot Jupiter could orbit before the host star pulled away too much mass from the planet.

    The authors defined a parameter ‘x’ for a given hot Jupiter to be x = a/aRoche, where ‘a’ is the planet’s observed semi-major axis. Based on the minimum distances in the above theories, we could predict that hot Jupiters that underwent disk migration would have a minimum x-value of x = aRoche/aRoche = 1. On the other hand, hot Jupiters that underwent eccentric migration would instead have a minimum x-value of x = 2aRoche/aRoche = 2. This x for a given planet is proportional to the planet’s orbital period ‘P’, its radius ‘R’, and its mass ‘M’ in the following way:

    And this x served as a key parameter in the authors’ statistical models!

    Toying with Bayesian Statistics

    Next question: how did today’s authors statistically model their data?

    4
    Figure 2: Probability distribution of x for each observation group, assuming that each hot Jupiter orbit was observed along the edge (like looking at the thin edge of a DVD). The bottom panel zooms in on the top one. Note how the samples have different minimum values! [Nelson et al. 2017]

    Short answer: with Bayesian statistics. Basically, the authors modeled how the parameter x is distributed within their planet sample with truncated power laws — so, x raised to some power, cut off between minimum and maximum x values. They split their sample of planets into two groups, based on the telescope and technique used to observe the planets: “RV+Kepler” and “HAT+WASP”. Figure 2 displays the distribution of x for each of the subgroups.

    The authors then used the Markov Chain Monte Carlo method (aka, MCMC; see the Bayesian statistics link above) to explore what sort of values of the power laws’ powers and cutoffs would well represent their data. Based on their chosen model form, they found that the RV+Kepler sample fit well with their model relating to eccentric migration. On the other hand, they found evidence that the HAT+WASP sample could be split into two populations: about 15% of those planets corresponded to disk migration, while the other 85% or so corresponded to eccentric migration.

    Remember that a major goal of today’s authors was to see if they could use this statistical approach to distinguish between planet populations in their sample … and in that endeavor, they were successful! The authors were thus optimistic about using this statistical technique for a much larger sample of hot Jupiters in the future, as oodles of data stream in from telescopes and surveys like KELT, TESS, and WFIRST over the next couple of decades.

    Their success joins the swelling toolbox of astrostatistics … and just in time! Telescopes of the present and very-near future are going to flood our computers with data — so unless we’re willing to examine every bright spot we observe in the sky by hand, we’ll need all the help from statistics that we can get!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:30 am on April 5, 2017 Permalink | Reply
    Tags: , , , , , Hot Jupiters   

    From astrobites: “Samples and Statistics: Distinguishing Populations of Hot Jupiters in a Growing Dataset” 

    Astrobites bloc

    Astrobites

    Apr 5, 2017
    Jamila Pegues

    Title: Evidence for Two Hot Jupiter Formation Paths
    Authors: Benjamin E. Nelson, Eric B. Ford, and Frederic A. Rasio
    First Author’s Institution: Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, IL, USA; Northwestern Institute for Complex Systems, IL, USA

    Status: Submitted to AJ, open access

    Frolicking through fields of data

    The future of astronomy observations seems as bright as the night sky… and just as crowded! Over the next decade, several truly powerful telescopes are set to launch (read about a good number of them here and also here). That means we’re going to have a LOT of data on everything from black holes to galaxies, and beyond – and that’s in addition to the huge fields of data from the past decade that we’re already frolicking through now. It’s certainly far more data than any one astronomer (or even a group of astronomers) wants to analyze one-by-one – that’s why these days, astronomers turn more and more to the power of astrostatistics to characterize their data.

    The author’s of today’s astrobite had that goal in mind. They explored a widely-applicable, data-driven statistical method for distinguishing different populations in a sample of data. In a sentence, they took a large sample of hot Jupiters and used this technique to try and separate out different populations of hot Jupiters, based on how the planets were formed, within their sample. Let’s break down exactly what they did, and how they did it, in the next few sections!

    Hot Jupiters are pretty cool

    First question: what’s a hot Jupiter, anyway?

    They’re actually surprisingly well-named: essentially, they are gas giant planets like Jupiter, but are much, much hotter. (Read all about them in previous astrobites, like this one and this other one!) Hot Jupiters orbit perilously close to their host stars – closer even than Mercury does in our own Solar System, for example. But it seems they don’t start out there. It’s more likely that these hot Jupiters formed out at several AU from their host stars, and then migrated inward into the much closer orbits from there.

    2
    Figure 1: A gorgeous artist’s impression of a hot Jupiter orbiting around its host star. Image credit goes to ESO/L. Calçada.

    As to why hot Jupiters migrate inward… well, it’s still unclear. Today’s authors focused on two migration pathways that could lead to two distinct populations of hot Jupiters in their sample. These migration theories, as well as what the minimum allowed distance to the host star (the famous Roche separation distance, aRoche) would be in each case, are as follows:

    Disk migration: hot Jupiters interact with their surrounding protoplanetary disk, and these interactions push their orbits inward. In this context, aRoche corresponds to the minimum distance that a hot Jupiter could orbit before its host star either (1) stripped away all of the planet’s gas or (2) ripped the planet apart.
    Eccentric migration: hot Jupiters start out on very eccentric (as in, more elliptical than circular) orbits, and eventually their orbits morph into circular orbits of distance 2aRoche. In this context, aRoche refers to the minimum distance that a hot Jupiter could orbit before the host star pulled away too much mass from the planet.

    The authors defined a parameter ‘x’ for a given hot Jupiter to be x = a/aRoche, where ‘a’ is the planet’s observed semi-major axis. Based on the minimum distances in the above theories, we could predict that hot Jupiters that underwent disk migration would have a minimum x value of x = aRoche/aRoche = 1. On the other hand, hot Jupiters that underwent eccentric migration would instead have a minimum x value of x = 2aRoche/aRoche = 2. This x for a given planet is proportional to the planet’s orbital period ‘P’, its radius ‘R’, and its mass ‘M’ in the following way:

    And this x served as a key parameter in the authors’ statistical models!

    Toying with Bayesian statistics

    Next question: how did today’s authors statistically model their data?

    4
    Figure 2: Probability distribution of x for each observation group, assuming that each hot Jupiter orbit was observed along the edge (like looking at the thin edge of a DVD). The bottom panel zooms in on the top one. Note how the samples have different minimum values! From Figure 1 in the paper.

    Short answer: with Bayesian statistics. Basically, the authors modeled how the parameter x is distributed within their planet sample with truncated power laws – so, x raised to some power, cutoff between minimum and maximum x values. They split their sample of planets into two groups, based on the telescope and technique used to observe the planets: “RV+Kepler” and “HAT+WASP”. Figure 2 displays the distribution of x for each of the subgroups.

    The authors then used the Markov Chain Monte Carlo method (aka, MCMC; see the Bayesian statistics link above!) to explore what sort of values of the power laws’ powers and cutoffs would well represent their data. Based on their chosen model form, they found that the RV+Kepler sample fit well with their model relating to eccentric migration. On the other hand, they found evidence that the HAT+WASP sample could be split into two populations: about 15% of those planets corresponded to disk migration, while the other 85% or so corresponded to eccentric migration.

    Remember that a major goal of today’s authors was to see if they could use this statistical approach to distinguish between planet populations in their sample… and in that endeavor, they were successful! The authors were thus optimistic about using this statistical technique for a much larger sample of hot Jupiters in the future, as oodles of data stream in from telescopes and surveys like KELT [North], TESS, and WFIRST over the next couple of decades.

    NASA/TESS

    NASA/WFIRST

    Their success joins the swelling toolbox of astrostatistics… and just in time! Telescopes of the present and very-near future are going to flood our computers with data – so unless we’re willing to examine every bright spot we observe in the sky by hand, we’ll need all the help from statistics that we can get!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:38 pm on January 20, 2017 Permalink | Reply
    Tags: , , , , , , HATnet, Hot Jupiters   

    From AAS NOVA: “Reinflating Giant Planets” 

    AASNOVA

    American Astronomical Society

    18 January 2017
    Susanna Kohler

    1
    Artist’s impression of a hot Jupiter exoplanet transiting across the face of its host star. [NASA/ESA/C. Carreau]

    Two new, large gas-giant exoplanets have been discovered orbiting close to their host stars. A recent study examining these planets — and others like them — may help us to better understand what happens to close-in hot Jupiters as their host stars reach the end of their main-sequence lives.

    2
    Unbinned transit light curves for HAT-P-65b. [Adapted from Hartman et al. 2016]

    Oversized Giants

    The discovery of HAT-P-65b and HAT-P-66b, two new transiting hot Jupiters, is intriguing. These planets have periods of just under 3 days and masses of roughly 0.5 and 0.8 times that of Jupiter, but their sizes are what’s really interesting: they have inflated radii of 1.89 and 1.59 times that of Jupiter.

    These two planets, discovered using the Hungarian-made Automated Telescope Network (HATNet) in Arizona and Hawaii, mark the latest in an ever-growing sample of gas-giant exoplanets with radii larger than expected based on theoretical planetary structure models.

    HATNet telescopes at Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona. Photo credit: Gaspar Bakos.pple-observatory-mount-hopkins-arizona-photo-credit-gaspar-bakos
    HATNet telescopes at Fred Lawrence Whipple Observatory, Mount Hopkins, Arizona. Photo credit: Gaspar Bakos

    HATnet, Mauna Kea Hawaii USA
    HATNet, Mauna Kea Hawaii USA

    What causes this discrepancy? Did the planets just fail to contract to the expected size when they were initially formed, or were they reinflated later in their lifetimes? If the latter, how? These are questions that scientists are only now starting to be able to address using statistics of the sample of close-in, transiting planets.

    Exploring Other Planets

    4
    Unbinned transit light curves for HAT-P-66b. [Hartman et al. 2016]

    Led by Joel Hartman (Princeton University), the team that discovered HAT-P-65b and HAT-P-66b has examined these planets’ observed parameters and those of dozens of other known close-in, transiting exoplanets discovered with a variety of transiting exoplanet missions: HAT, WASP, Kepler, TrES, and KELT. Hartman and collaborators used this sample to draw conclusions about what causes some of these planets to have such large radii.

    The team found that there is a statistically significant correlation between the radii of close-in giant planets and the fractional ages of their host stars (i.e., the star’s age divided by its full expected lifetime). The two newly discovered hot Jupiters with inflated radii, for instance, are orbiting stars that are roughly 84% and 83% through their life spans and are approaching the main-sequence turnoff point.

    6
    Fractional age of the host stars of close-in transiting exoplanets vs. the planet’s radius. There is a statistically significant correlation between age and planet radius. [Adapted from Hartman et al. 2016]

    Late-Life Reinflation

    Hartman and collaborators propose that the data support the following scenario: as host stars evolve and become more luminous toward the ends of their main-sequence lifetimes, they deposit more energy deep into the interiors of the planets closely orbiting them. These close-in planets then increase their equilibrium temperatures — and their radii reinflate as a result.

    Based on these results, we would expect to continue to find hot Jupiters with inflated radii primarily orbiting closely around older stars. Conversely, close-in giant planets around younger stars should primarily have non-inflated radii. As we continue to build our observational sample of transiting hot Jupiters in the future, we will be able to see how this model holds up.

    Citation

    J. D. Hartman et al 2016 AJ 152 182. doi:10.3847/0004-6256/152/6/182

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

     
  • richardmitnick 12:26 pm on June 22, 2016 Permalink | Reply
    Tags: , , , , Hot Jupiters, Where the Wild (Planet)Things Are   

    From Astrobites: Where the Wild (Planet)Things Are 

    New research shows hot Jupiters find safety in numbers. According to radial velocity data, these giant exoplanets are more commonly found around stars in open clusters.

    Source: Where the Wild (Planet)Things Are

    Title: Search for giant planets in M67 III: excess of hot Jupiters in dense open clusters
    Authors: A. Brucalassi, L. Pasquini, R. Saglia, M.T. Ruiz, P. Bonifacio, I. Leão, B.L. Canto Martins, J.R. de Medeiros, L. R. Bedin, K. Biazzo, C. Melo, C. Lovis, and S. Randich

    First Author’s Institution: Max-Planck für extraterrestrische Physik, Garching bei München, Germany

    Status: Accepted for publication in A&A Journal Letters

    If you wanted to discover a new giant exoplanet, where would you look? New research, shows that star clusters are a good place to start, at least if you want to look for giant exoplanets close to their host star.

    Hot Jupiters are a breed of exoplanets that have masses about or larger than Jupiter and orbit a star in 10 days or less (for comparison, Mercury takes 88 days to go around the Sun). When they were first discovered, they posed a problem to planet formation models as it was thought gas giants could only form far from their host star where it was cool enough for ices to form, which allows for larger planets to be made. Since then, studies have shown these planets could form far out and migrate inwards over their lifetime. This can happen through interactions with the disk in which the planet forms (known as Type II migration), or through gravitational scattering with other planets or nearby stars.

    Brucalassi and her team decided to investigate an open cluster in the Milky Way (Messier 67) to look for hot Jupiters. Over several years they used three different telescopes (the ESO 3.6m telescope, the Hobby Eberly Telescope and the TNG on La Palma of the Canary Islands) to take high-precision spectra of 88 stars, 12 of which are binary stars. This spectra could then be analyzed for small blue- and redshifts which indicate the star is moving slightly. In this case, that movement is caused by the presence of another body, the exoplanet. This method is known as the radial velocity method and is the method that was used in the first exoplanet discoveries. To make sure that each star’s own activity wasn’t affecting its spectra, the group measured the Hα line which shows how active the star’s chromosphere is. Figure 1 shows an example of the radial velocity measurements.

    1
    Figure 1: Radial velocity measurements for YBP401. The coloured dots represent the different telescopes the measurements were made at. The measurements show an exoplanet with a period of just 4.08 days.

    The group’s measurements revealed a new exoplanet around the main sequence star YBP401. They were also able to get better measurements on two stars (YBP1194 and YBP1514) with known hot Jupiters. This brought the total number of hot Jupiters to 3 out of 88 stars. Although 3 might not seem like a very big number, it is larger than the number of hot Jupiters found around field stars (stars not in clusters). For the statistical analysis, Brucalassi compares the number of exoplanets with the number of main sequence and subgiant stars, i.e. stars that are not yet at the ends of their lives. Of the 88 stars, 66 are main sequence or subgiant, and of those only 53 are not binary stars. Most radial velocity studies choose to not observe binary stars so it is important to compare numbers with that in mind. A previous study from 2012 found a hot Jupiter frequency of 1.2% ± 0.38 around field stars. Brucalassi finds 4.5+4.5-2.5% when comparing with only single stars (not including binaries) in M67. To compare with statistics from the Kepler mission, binaries are included, as Kelper also surveys binaries, and the percentage for hot Jupiters in a cluster is 5.6+5.4-2.6%. The Kepler mission finds a frequency of hot Jupiters of just ~0.4%, which is considerably lower. And this trend isn’t seen just in M67. Combining radial velocity surveys for the clusters M67, Hyades, and Praesepe, there are 6 hot Jupiters in 240 surveyed stars, whereas the study from 2012 found only 12 in survey of 836 field stars.

    It’s known that systems with more metals tend to produce more planets and the star’s mass may also have an effect on planet production. However, the clusters stars and field stars are on average the same mass, so this alone cannot account for the differneces. M67 is also at solar metallicity (i.e. it’s stars tend to have the same amount of metals as our Sun) so this can also not account for the excess of hot Jupiters. Brucalassi concludes that the high number of hot Jupiters is due to the environment. Past simulations show that stars in a crowded cluster environment will experience at least one close encounter with another star, which is all that is needed to drive a Jupiter in to a closer orbit. This new research gives further evidence to this theory, putting us one step closer to understanding how exoplanets can form.

    3
    Figure 2: An artist’s rendition of the new hot Jupiter. Click on the image for a full animated video of the M67 cluster. Courtesy of the ESO press release (#eso1621).

     
  • richardmitnick 4:49 pm on March 31, 2016 Permalink | Reply
    Tags: , , , Hot Jupiters, TYC 3667-1280-1   

    From astrobites: “A Warm Jupiter around an Evolving Star: Exploring Planet Migration” 

    Astrobites bloc

    Astrobites

    Mar 31, 2016
    Matthew Green

    Title: TAPAS IV. TYC 3667-1280-1 b – the most massive red giant star hosting a warm Jupiter
    Authors: A. Niedzielski, E. Villaver, G. Nowak, M. Adamów, G. Maciejewski, K. Kowalik, A. Wolszczan, B. Deka-Szymankiewicz, M. Adamczyk
    First Author’s Institution: Toruń Centre for Astronomy, Nicolaus Copernicus University, Toruń, Poland
    Status: Accepted by A&A

    Planetary systems are dynamic places. Some planetary orbits change over time, moving the planet either closer in towards the star or further out. Not only that, but the stars in the centre of planetary systems will eventually evolve off the main sequence, growing into giants and then, in most cases, collapsing into white dwarfs. This can significantly change the planetary system as a whole, in some cases leading to planets being swallowed by their host stars or ejected from the system. Of course, these changes occur over timescales of millions to billions of years.

    There has recently been a spike of interest in what happens to planets as their host star evolves, inspired by the discovery of a system of disintegrating planets around a white dwarf. Today’s paper introduces TYC 3667-1280-1, a Jupiter-mass exoplanet whose host star is in the process of evolving into a giant. The authors believe that the planet is of interest not only because of its evolving host, but also because of the planet’s potentially revealing migration history.

    Stars as Homes for Habitable Planetary Systems. JPL-Caltech
    Stars as Homes for Habitable Planetary Systems. JPL-Caltech

    Warm Jupiters and the Kozai-Lidov mechanism

    Planets of Jupiter mass, like TYC 3667-1280-1, are thought to form far out in the system, where there is more material from which they can form. However, we have seen many Jupiter-mass planets which are incredibly close to their host star, often much closer than the Earth is to the Sun. Consequentially these systems have very short orbital periods. The so-called hot Jupiters have orbits shorter than 10 days, while “warm Jupiters” have orbits of 10-100 days (compare this to Jupiter’s orbital period of 12 years).

    How did these planets end up so close to their host stars? Warm and hot Jupiters may have travelled inwards by different means. Jupiter-mass planets can migrate inwards by being gravitationally pushed to high eccentricities (highly elliptical orbits). However, many systems in both classes have orbits with very low (their orbits are almost perfect circles). In hot Jupiters, the planet’s orbit can be “circularised” again by the gravitational pull of the star — however, this doesn’t work as well across the distances at which warm Jupiters orbit. How, then, do we explain the low eccentricities in some warm Jupiters?

    There’s also a second mystery around warm Jupiters. We see fewer hot and warm Jupiters around evolved or evolving stars than we do around main sequence stars. For hot Jupiters this is easily explained: for most of these systems, the planet is close enough to have been swallowed by its host star. However, warm Jupiters are further out from their stars, and so we would expect them to last longer than they seem to.

    Both of these problems might be explained by an effect known as the Kozai-Lidov mechanism. This is a tidal effect that occurs in hierarchical three-body systems – that is, systems in which two of the bodies (in this case, a star and a planet) are in a tight orbit around each other, with a third object in a wider orbit around the two (a potentially unseen companion such as a brown dwarf). If the orbit of the outer object is tilted relative to the orbits of the inner binary, the gravity of the outer object pulls on the inner pair in such a way that the eccentricity of their orbits fluctuates. (For more detail on the Kozai-Lidov mechanism, see Erika Nesvold’s section in this astrobite.) The low-eccentricity warm Jupiters that we see could simply be those in a low-eccentricity phase of these fluctuations.

    Conversely, when the planet fluctuates up to a highly eccentric orbit it will pass much closer to its host star, causing it to be swallowed by the expanding star much earlier than it would be if there were no Kozai-Lidov mechanism in play. In fact, for a sample system their simulations showed the planet might be swallowed by the time the star grew to 5 solar radii, compared to 40 solar radii for the same system with no Kozai-Lidov mechanism.

    TYC 3667-1280-1

    Enter TYC 3667-1280-1, whose star has a radius of 6.3 solar radii — putting it just inside the range of what should have been swallowed if the Kozai-Lidov mechanism is at work in this system. In other respects TYC 3667-1280-1 appears to be a typical warm Jupiter, having the low eccentricity (0.036 in this case) that could imply the Kozai-Lidov mechanism is at work. Further studies of TYC 3667-1280-1 could help clear up this seeming conflict, as well as helping us to understand the Kozai-Lidov mechanism further.

    The science team:
    A. Niedzielski1, E. Villaver2, G. Nowak3; 4; 1, M. Adamów5; 1, G. Maciejewski1, K. Kowalik6, A. Wolszczan7; 8, B.
    Deka-Szymankiewicz1, and M. Adamczyk1
    1 Toru´n Centre for Astronomy, Faculty of Physics, Astronomy and Applied Informatics, Nicolaus Copernicus University in Toru´n,
    Grudziadzka 5, 87-100 Toru´n, Poland. e-mail: Andrzej.Niedzielski@umk.pl
    2 Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain. e-mail:
    Eva.Villaver@uam.es
    3 Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain.
    4 Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain.
    5 McDonald Observatory and Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1402, Austin, Texas,
    78712-1206, USA.
    6 National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign, 1205 W Clark St, MC-257, Urbana,
    IL 61801, USA
    7 Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802,
    USA. e-mail: alex@astro.psu.edu
    8 Center for Exoplanets and Habitable Worlds, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802,
    USA.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:59 am on March 10, 2016 Permalink | Reply
    Tags: , , Hot Jupiters,   

    From phys.org: “Astronomers discover two new ‘hot Jupiter’ exoplanets” 

    physdotorg
    phys.org

    March 10, 2016
    Tomasz Nowakowski

    Hot Jupiter orbiting one star in a binary system
    Hot Jupiter orbiting one star in a binary system (not part of this work)

    A team of Chilean astronomers recently detected two new hot Jupiters using the data from NASA’s Kepler spacecraft operating in a new mission profile called K2.

    NASA Kepler Telescope
    NASA/Kepler

    The planets, designated EPIC210957318b and EPIC212110888b, were discovered via the radial velocity method, and are excellent candidates for further orbital and atmospheric characterization via detailed follow-up observations. A research paper describing the discovery appeared online on Mar. 5, on the arXiv server.

    The so-called “hot Jupiters” are gas giant planets, similar in characteristics to the solar system’s biggest planet, with orbital periods of less than 10 days. They have high surface temperatures as they orbit their parent stars very closely—between 0.015 and 0.5 AU—while Jupiter orbits the sun at 5.2 AU. To date, about 250 transiting “hot Jupiters” have been found, mostly by ground-based photometric surveys. Now, the researchers have made use of a space-borne telescope to detect new, interesting hot giant exoworlds.

    K2 is a repurposed mission of the Kepler spacecraft to perform high-precision photometry of selected fields in the ecliptic, following the failure of two reaction wheels in 2013. Due to this malfunction, observations are currently conducted only within the orbital plane of the spacecraft, which approximates to the ecliptic. However, despite these difficulties, K2 has managed to detect 234 planetary candidates in the first year of the mission.

    The researchers, led by Rafael Brahm of the Pontifical Catholic University of Chile, have analyzed the photometric data of K2’s two observation campaigns and discovered that the stars EPIC210957318 and EPIC212110888 show significant periodic signals every four and three days, respectively.

    “Both of these systems were selected as strong Jovian planetary candidates based on their transit properties (depths, shapes and durations), and due to the lack of evident out of transit variations,” the paper reads.

    Next, the researchers acquired high-resolution spectra of the two candidates, with three different stabilized spectrographs mounted on telescopes at the [ESO]La Silla Observatory in Chile. These instruments were helpful in measuring the radial velocity variation of the stellar hosts produced by the gravitational pull of orbiting planets.

    ESO LaSilla
    ESO La Silla

    According to the paper, the smaller planet of the newly discovered duo, named EPIC210957318b, orbits its parent sun-like star, located about 970 light years from the Earth, every 4.1 days. The mass of this exoplanet is between the Saturn and Jupiter masses (approximately 0.65 Jupiter masses) and its radius is slightly larger than the one of the solar system’s largest planets. The temperatures on this planet range from 584 to 939 degrees Celsius.

    EPIC212110888b is more massive and larger than Jupiter. Having a mass of about 1.63 Jupiter masses, this planet orbits its host star every three days and is even hotter than EPIC210957318b, with temperatures spanning from 932 to 1,430 degrees Celsius. The star, slightly more massive than sun, lies some 1,270 light years away from our planet.

    Both planets have similar densities, close to half of Jupiter’s. The scientists noted that the physical and orbital properties of both of these extrasolar systems are typical of the population of known hot Jupiters. They also concluded that these two exoplanets are interesting candidates for follow-up studies.

    “The low density of EPIC210957318b combined with the relatively small radius of its host star implies a scale height of 340 km and a transmission spectroscopic signal of 744 ppm (assuming an H2 dominated atmosphere and a signal of five scale-heights), which means that this system is a good target to be observed via transmission spectroscopy to characterize its atmosphere,” they wrote.

    More information: An independent discovery of two hot Jupiters from the K2 mission, arXiv:1603.01721 [astro-ph.EP] arxiv.org/abs/1603.01721.

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 5:08 pm on January 27, 2016 Permalink | Reply
    Tags: , , , Hot Jupiters   

    From AAS NOVA: “Hot Jupiters Aren’t As Lonely As We Thought” 

    AASNOVA

    American Astronomical Society

    27 January 2016
    Susanna Kohler

    Hot Jupiter orbiting one star in a binary system
    This median-stacked image, obtained with adaptive optics, shows one of the newly-discovered stellar companions to a star hosting a hot Jupiter. The projected separation is ~180 AU. [Ngo et al. 2015]

    The Friends of Hot Jupiters (FOHJ) project is a systematic search for planetary- and stellar-mass companions in systems that have known hot Jupiters — short-period, gas-giant planets. This survey has discovered that many more hot Jupiters may have companions than originally believed.

    Missing Friends

    FOHJ was begun with the goal of better understanding the systems that host hot Jupiters, in order to settle several longstanding issues.

    The first problem was one of observational statistics. We know that roughly half of the Sun-like stars nearby are in binary systems, yet we’ve only discovered a handful of hot Jupiters around binaries. Are binary systems less likely to host hot Jupiters? Or have we just missed the binary companions in the hot-Jupiter-hosting systems we’ve seen so far?

    An additional issue relates to formation mechanisms. Hot Jupiters probably migrated inward from where they formed out beyond the ice lines in protoplanetary disks — but how?

    Observations reveal two populations of hot Jupiters: those with circular orbits aligned with their hosts’ spins, and those with eccentric, misaligned orbits. The former population support a migration model dominated by local planet-disk interactions, whereas the latter population suggest the hot Jupiters migrated through dynamical interactions with distant companions. A careful determination of the companion rate in hot-Jupiter-hosting systems could help establish the ability of these two models to explain the observed populations.

    Search for Companions

    The FOHJ project began in 2012 and studied 51 systems hosting known, transiting hot Jupiters — with roughly half on circular, aligned orbits and half on eccentric, misaligned orbits. The survey consisted of three different, complementary components:

    Study 1
    Lead author: Heather Knutson (Caltech)
    Technique: Long-term radial velocity monitoring
    Searching for: Planetary companions at 1–20 AU from the star
    Study 2
    Lead author: Henry Ngo (Caltech)
    Technique: Adaptive optics imaging
    Searching for: Stellar companions at 50–2000 AU from the star
    Study 3
    Lead author: Danielle Piskorz (Caltech)
    Technique: Spectroscopy
    Searching for: Any additional stellar companions at <125 AU from the star

    Migration Implications

    Using these three different techniques, the team found a significant number of both planetary and stellar companions that had not been previously detected. After correcting their results for completeness, they found a multiple-star rate of ~50% for these systems, resolving the problem of the missing companions. So really, we just weren’t looking hard enough for the companions previously.

    Intriguingly, the binary companion rate found for these hot Jupiter systems is higher than the average rate for the field stars (which is below 25% for the semimajor-axis range the FOHJ studies are sensitive to). This suggests that companion stars may indeed play a role in hot Jupiter formation and migration.

    That said, none of the three studies found a significant difference in the binary fraction for aligned versus misaligned hot Jupiters — which means that the answer is not as simple as thought, with companion stars causing the misaligned planets. Thus, while hot Jupiters’ “friends” may play a role in their formation and migration, we still have work to do in understanding what that role is.

    Citation

    Danielle Piskorz et al 2015 ApJ 814 148. doi:10.1088/0004-637X/814/2/148
    Henry Ngo et al 2015 ApJ 800 138. doi:10.1088/0004-637X/800/2/138
    Heather A. Knutson et al 2014 ApJ 785 126. doi:10.1088/0004-637X/785/2/126

    See the full article here .

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  • richardmitnick 10:02 am on December 31, 2015 Permalink | Reply
    Tags: , , , Hot Jupiters   

    From CFHT: “Hot Jupiters courting baby stars?” 

    CFHT icon
    Canada France Hawaii Telescope

    September 9th 2015 [Some CFHT articles were not properly made public. They promised to corect this.]

    Contacts:
    Dr. Claire Moutou (CFHT, Hawaii)
    moutou@cfht.hawaii.edu
    1-808-885-7944

    Dr. Lison Malo (CFHT, Hawaii)
    malo@cfht.hawaii.edu
    1-808-885-7944

    Dr. Jean-Francois Donati (IRAP, Toulouse, France)
    jean-francois.donati@irap.omp.eu
    33-561-332-917

    Temp 1
    Formation of stars and their planets in the Taurus nursery as seen at millimeter wavelengths by the APEX telescope in Chile (credits ESO/APEX)

    Although first detected 20 years ago, hot Jupiters are still enigmatic bodies. These celestial objects are giant Jupiter-like exoplanets that orbit 20 times closer to their host stars than the Earth does to the Sun. Using the ESPaDOnS spectro-polarimeter on the Canada-France-Hawaii Telescope, the Matysse(1) team led by Dr J.-F. Donati (Toulouse, CNRS) reports the preliminary evidence that a hot Jupiter orbits a 2-My star of the Taurus star forming region.

    CFHT ESPaDOns preferred
    CFHT ESPaDOns
    ESPaDOnS

    This planet, yet to be confirmed, has a mass of 1.4 Jupiter mass and a 6-day period orbit and is unveiled by the gravitational pull it imprints on its star(2), once the stellar activity features are modeled. This discovery(3) could help us better understand how planetary systems like (or unlike) the solar system form and evolve into maturity. This could also be the first exoplanet ever revealed by CFHT, a nice introduction to the coming SPIRou(4) planet search survey.

    In our solar system, rocky planets like the Earth or Mars are found near the Sun whereas giant planets like Jupiter and Saturn orbit much further out. “Hence the surprise in 1995 when Mayor & Queloz first unveiled a giant planet sitting very close to its host star” says Dr C. Moutou, CNRS astronomer at CFHT and co-author of this new study. Since then, astronomers demonstrated that such planets must form in the outer regions of the protoplanetary disc, then migrate inwards and yet avoid falling into their host star. This could happen either very early in their lives, when still embedded within their primordial disc. Or much later, once multiple planets are formed and mutually interact in a rather unstable choreography – with some being pushed inwards at the immediate vicinity of their stars.

    An international team of astronomers led by Dr J.-F. Donati just secured preliminary evidence supporting the first of these two scenarios. Using ESPaDOnS, a spectropolarimeter built by IRAP / OMP for the CFHT, they looked at newly-born stars in the Taurus stellar nursery about 450 light-years away from us. They showed that the latest baby star they scrutinized, nicknamed V830 Tau, exhibits signatures that closely resemble those caused by a 1.4 Jupiter-mass planet orbiting 15 times closer to its host star than the Earth does to the Sun. This discovery, published in MNRAS, provides preliminary evidence that hot Jupiters may be extremely young and far more frequent around very young stars than around mature Sun-like stars.

    Although potentially very informative about planet formation, young stars are extremely challenging to observe. “Being enormously active and strongly magnetic, baby stars are covered with huge spots hundreds of times wider than those of our Sun, which generate perturbations in their spectra much larger than those caused by orbiting planets. As a result, their planets are quite tricky to detect, even in the case of hot Jupiters”, outlines E. Hebrard, PhD student at IRAP / OMP and co-author of the study. To address this issue, the team initiated the MaTYSSE survey aimed at mapping the surfaces of baby stars and at looking for the potential presence of hot Jupiters. “By monitoring these stars and using tomographic techniques inspired from medical imaging, we can unveil how dark and bright features are distributed across their surfaces, and how their magnetic fields expand into space. This modeling allows us to compensate for the perturbations that spots and fields generate in the spectra of young stars, and thus to regain the power of diagnosing the presence of close-in giant planets”, explains Dr G. Hussain (ESO, UFTMiP), co-author of the study. In the case of V830 Tau, the authors accurately modeled the surface field and spots in order to clean out their polluting effects, enabling them to discover the much weaker signal that hints at the presence of a giant planet. Although more data are required for a definite validation, this promising first result clearly demonstrates that the technique the team devised is powerful enough to solve the puzzling question of how hot Jupiters form. ” SPIRou, the new instrument currently built for CFHT by our team and scheduled for first light in 2017, will offer vastly superior performances thanks to its operation at near infrared wavelengths, at which young stars are far brighter, and will allow us to address this long-standing problem with unprecedented accuracy”, Dr J.-F. Donati concludes.

    2
    ESPaDOnS observations of V830 Tau – a baby star in the Taurus nursery. Once the polluting effect of spots is removed, the residual shift of the spectrum (red dots and error bars) varies with time with a 6-day period. This spectral motion is compatible with that expected from a 1.4 Jupiter-mass planet orbiting at only 1/15 of the Sun-Earth distance (light blue curve). More densely-sampled observations are necessary to validate this preliminary result.

    Additional information

    • 1. Matysse (Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets) is a CFHT Large Program started in 2013 with ESPaDOnS. Matysse is a collaboration led by J.F. Donati (IRAP, Obs Midi-Pyrenees, France) with astronomers from IPAG (Grenoble, F), ENS (Lyon, F), CEA (Saclay, F), LAM (Marseille, F), OCA (Nice, F), UdM (Montreal, C), UFMG (Belo Horizonte, B), ASIAA (Taipei, T), NAO (Beijing, C) and many associated scientists outside the CFHT community.
    • 2. The radial-velocity method uses the gravitational pull on the star by the planet modulated by its orbital motion, and measures the resulting spectral shift of the star with respect to the observer using the Doppler effect. This effect is of the order of 100 m/s for a hot Jupiter as the putative V 830 b and is repeatable at the period of the orbit – here, about 6 days.
    • 3. The full paper is accepted in the Monthly Notices of the Royal Astronomical Society (MNRAS, Oxford University Press); it is entitled: “Magnetic activity and hot Jupiters of young Suns: the weak-line T Tauri stars V819 Tau and V830 Tau”, by J.-F. Donati, E. Hebrard, G. Hussain, C. Moutou, L. Malo, K. Grankin, A. Vidotto, S. Alencar, S.G. Gregory, MM. Jardine, G. Herczeg, J. Morin, R. Fares, F. Menard, J. Bouvier, X. Delfosse, R. Doyon, M. Takami, P. Figueira, P. Petit, I. Boisse and the MaTYSSE collaboration, and is accessible here.
    • 4. SPIRou i is a near-infrared spectropolarimeter and a high-precision velocimeter optimized for both the detection of habitable Earth twins orbiting around nearby red dwarf stars, and the study of forming Sun-like stars and their planets. SPIRou is managed in the framework of an international consortium led by France and involving, in addition to the Canada-France-Hawaii Telescope (CFHT), Canada, Switzerland, Brazil, Taiwan and Portugal. The construction of SPIRou has started in 2015, with integration in Toulouse, France, scheduled for 2016 and first light at CFHT for 2017.

    See the full article here .

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    The CFH observatory hosts a world-class, 3.6 meter optical/infrared telescope. The observatory is located atop the summit of Mauna Kea, a 4200 meter, dormant volcano located on the island of Hawaii. The CFH Telescope became operational in 1979. The mission of CFHT is to provide for its user community a versatile and state-of-the-art astronomical observing facility which is well matched to the scientific goals of that community and which fully exploits the potential of the Mauna Kea site.

    CFHT Telescope
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