From SDSS: “The APOGEE-South First Light Field”
March 29, 2017
This post was written by Carlos Roman (Instituto de Astronomía, UNAM, Mexico), with help from Roger Cohen (Universidad de Concepción, Chile) and Guy Stringfellow (University of Colorado). Spanish by Carlos Roman.
The 30 Doradus region in the Large Magellanic Cloud (otherwise known as the Tarantula Nebula) was selected as the First Light plate for the APOGEE South Survey at Las Campanas Observatory. Several reasons stand out for this choice:
Tarantula Nebula, Hubble 2009. Credit NASA, ESA, and F. Paresce INAF-IASF, Bologna, Italy, R. O’Connell University of Virginia, Charlottesville, and the Wide Field Camera 3 [WFC3]Science Oversight Committee
Several reasons stand out for this choice:
The Large and the Small (LMC, SMC) Magellanic Clouds are among the most representative features of the South Hemisphere sky.
This ground-based image of the Large Magellanic Cloud was taken by German astrophotographer Eckhard Slawik. Image via ESA
Small Magellanic Cloud. Credit ESA/Hubble and Digitized Sky Survey 2.
They are among the handful of galaxies visible to the unaided human eye and are well known to the public in all Austral regions of the planet. The Magellanic Clouds are also the closest members in the Local Group of the Milky Way, which means they are the closest extragalactic environments to which we can compare our own, and therefore they have been the subject of copious studies, that include comprehensive, multi-wavelength surveys both ground and space-based, with facilities like the ESO-Vista Telescope, the Spitzer, Herschel and GALEX space observatories.
The Large Magellanic Cloud is particularly famous for its star formation activity. Despite being an irregular, relatively small galaxy, its star forming rate is extremely high. The molecular gas complexes in the LMC host some of the brightest stellar nurseries we can observe, and this is because they produce large numbers of massive stars. In fact, some of the most massive stars known are born in the LMC and in particular, they are being born in the 30 Doradus region, also known as the Tarantula Nebula, a beautiful ionized Hydrogen (HII) region partly illuminated by the star R136 group in the stellar cluster NGC 2070. This group contains about 10 of the most massive stars known, including the source R136a1, with an estimated mass of over 300 solar masses and a luminosity almost 9 millon times higher than our Sun’s. R136a1 is currently the most massive star known to date.
The LMC will be well covered in the APOGEE-2S survey. APOGEE will provide with infrared, high resolution spectra for thousands of stars in both Magellanic Clouds, which will provide an unprecedented database that will allow the reconstruction of their star formation and chemical evolution histories, allowing us to compare them with those of the Milky Way.
We chose the 30 Doradus region as the First Light plate for the APOGEE2S survey because of its importance as an astrophysical subject but also because of its beauty as illustrated in the following three image, where we have highlighted the field of view of the region we will observe with APOGEE, centered close to 30 Doradus.
DSS optical map of the LMC. We can distinguish the main stellar population of the cloud and several HII regions seen as gaseous bubbles. Image Credit: Carlos Roman, SDSS-IV and DSS.
The LMC as seen by the SAGE Legacy Survey of the galaxy made by the Spitzer Space Telescope: it shows in magnificient detail, the glow from gaseous regions illuminated by recently formed stars across the whole galaxy. Image Credit: Carlos Roman, SDSS-IV and Spitzer.
The same region but as seen with the Herschel Space Telescope in the Far-Infrared, this time tracing the complex structure of the interstellar medium of the LMC, seen as an intricated network of bubbles and filaments excavated by the winds of the massive stars and their clusters. Image Credit: Carlos Roman, SDSS-IV and Herschel.
Below we show a close-up of the 30 Doradus region and its surroundings, where we have outlined the field of view of the APOGEE spectrograph from Las Campanas Observatory 2.5m Dupont telescope. This field of view spans over 3 square degrees, 16 times the area of the full Moon. Inside this area, we have obtained spectra for 270 scientific targets, which we have also sketched in the map with different colored symbols.
Plot showing locations of proposed fibers on plate. Image Credit Carlos Roman.
The list of targets include:
a) 26 Luminous Blue Variables and Wolf Rayet star candidates, including R136a1. These are very massive sources, which are very short lived and formed very recently, so they trace the current episode in chemical evolution in the LMC as well as crucial information on the kinematics and properties of the massive clusters in which they form. These stars are the evolved stages of very massive stars and they are known to have large variations in brightness due to the fact that they are expelling their external layers by powerful winds. The Milky Way star Eta Carinae is a well known example of this kind of star. LBV stars also very characteristic spectra, with lines that present what is known as a P-Cygni profile, which appears both as an emission and absorption. These features indicate, precisely, the physical processes relevant to the winds.
b) 55 additional massive (OB) star candidates in the 30 Dor and surrounding star forming complexes. These targets were selected from the compilation of A. Bonanos, based on infrared photometry from the Spitzer SAGE Legacy Survey of the LMC (2009 AJ, 138, 1003), and from the optical spectroscopic survey of the N159/N160 star forming complexes -located South of 30 Dor- by C. Fariña (2009 AJ, 138, 2).
c) 42 blue, red and yellow Supergiants. These stars are giant and supergiant (known as Class I and II) equivalents of dwarf stars like our Sun. Blue stars are typically tens to hundreds of times more massive than the Sun. Yellow stars are closer in mass to our Sun, and red stars are stars made from only a fraction of a solar mass.
b) 80 red giant and 26 main-sequence stars from the mainstream population of the LMC, selected from near-IR photometry. These sources will provide a first look at the kinematics, the chemical abundances and the metallicity distribution function in the stellar populations of the LMC. There is an important link between these populations and the massive stars we are studying, as the first ones were most likely originated in stellar clusters like those hosting the massive stars.
c) 40 targets associated to local ISM regions, mostly HII regions associated with massive star clusters. These targets will provide important information about the properties of the interstellar medium (gas and dust) in the LMC, which can be traced by specific features in the spectra, like the so-called diffuse interstellar bands, but also by absorption features that are produced by carbon and other metals in the dust. The ability of APOGEE to provide information on the radial velocities of the gas will provide crucial information about the kinematical structure of the gas in the LMC, and how the properties of the interstellar medium relate to the diversity of environments present in the galaxy.
The first light data was taken earlier this month. Below we show a composite with the Herschel data, fibres overlaid and some examples of the spectral data that was obtained.
Here is a link to the press release about this first light for APOGEE South.
See the full article here .
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After nearly a decade of design and construction, the Sloan Digital Sky Survey saw first light on its giant mosaic camera in 1998 and entered routine operations in 2000. While the collaboration and scope of the SDSS have changed over the years, many of its key principles have stayed fixed: the use of highly efficient instruments and software to enable astronomical surveys of unprecedented scientific reach, a commitment to creating high quality public data sets, and investigations that draw on the full range of expertise in a large international collaboration. The generous support of the Alfred P. Sloan Foundation has been crucial in all phases of the SDSS, alongside support from the Participating Institutions and national funding agencies in the U.S. and other countries.
The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.
In its first five years of operations, the SDSS carried out deep multi-color imaging over 8000 square degrees and measured spectra of more than 700,000 celestial objects. With an ever-growing collaboration, SDSS-II (2005-2008) completed the original survey goals of imaging half the northern sky and mapping the 3-dimensional clustering of one million galaxies and 100,000 quasars. SDSS-II carried out two additional surveys: the Supernova Survey, which discovered and monitored hundreds of supernovae to measure the expansion history of the universe, and the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which extended SDSS imaging towards the plane of the Galaxy and mapped the motions and composition of more than a quarter million Milky Way stars.
SDSS-III (2008-2014) undertook a major upgrade of the venerable SDSS spectrographs and added two powerful new instruments to execute an interweaved set of four surveys, mapping the clustering of galaxies and intergalactic gas in the distant universe (BOSS), the dynamics and chemical evolution of the Milky Way (SEGUE-2 and APOGEE), and the population of extra-solar giant planets (MARVELS).
The latest generation of the SDSS (SDSS-IV, 2014-2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its revolutionary infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).
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