- ID:
- ivo://CDS.VizieR/J/ApJS/228/24
- Title:
- GALAH semi-automated classification scheme
- Short Name:
- J/ApJS/228/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way using the fossil remnants of disrupted star formation sites that are now dispersed around the Galaxy. It is targeting a randomly selected magnitude-limited (V<=14) sample of stars, with the goal of observing one million objects. To date, 300000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines, and we need to know about them. We present a semi-automated classification scheme that identifies different types of peculiar spectral morphologies in an effort to discover and flag potentially problematic spectra and thus help to preserve the integrity of the survey results. To this end, we employ the recently developed dimensionality reduction technique t-SNE (t-distributed stochastic neighbor embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighborhoods of spectra. We find that the majority (178483) of the 209533 Galah spectra considered in this study represents normal single stars, whereas 31050 peculiar and problematic spectra with very diverse spectral features pertaining to 28579 stars are distributed into 10 classification categories: hot stars, cool metal-poor giants, molecular absorption bands, binary stars, H{alpha}/H{beta} emission, H{alpha}/H{beta} emission superimposed on absorption, H{alpha}/H{beta} P-Cygni, H{alpha}/H{beta} inverted P-Cygni, lithium absorption, and problematic. Classified spectra with supplementary information are presented in the catalog, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution.
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Search Results
232. GALAH Survey DR2
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/4513
- Title:
- GALAH Survey DR2
- Short Name:
- J/MNRAS/478/4513
- Date:
- 04 Feb 2022 00:12:04
- Publisher:
- CDS
- Description:
- The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way, designed to deliver complementary chemical information to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342 682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction, and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multistep approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (Teff, logg, [Fe/H], [X/Fe], vmic, vsini, A_KS_) for a representative training set of stars. This information is then propagated to the whole sample with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D marcs stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.
- ID:
- ivo://CDS.VizieR/J/MNRAS/487/2474
- Title:
- GALAH unresolved triple Sun-like star
- Short Name:
- J/MNRAS/487/2474
- Date:
- 02 Mar 2022 00:37:36
- Publisher:
- CDS
- Description:
- The latest Gaia data release enables us to accurately identify stars that are more luminous than would be expected on the basis of their spectral type and distance. During an investigation of the 329 best solar twin candidates uncovered among the spectra acquired by the GALAH survey, we identified 64 such overluminous stars. In order to investigate their exact composition, we developed a data-driven methodology that can generate a synthetic photometric signature and spectrum of a single star. By combining multiple such synthetic stars into an unresolved binary or triple system and comparing the results to the actual photometric and spectroscopic observations, we uncovered 6 definitive triple stellar system candidate and an additional 14 potential candidates whose combined spectrum mimics the solar spectrum. Considering the volume correction factor for a magnitude-limited survey, the fraction of probable unresolved triple stars with long orbital periods is 2 per cent. Possible orbital configurations of the candidates were investigated using the selection and observational limits. To validate the discovered multiplicity fraction, the same procedure was used to evaluate the multiplicity fraction of other stellar types.
- ID:
- ivo://CDS.VizieR/VII/209A
- Title:
- Galaxies Behind the Milky Way
- Short Name:
- VII/209A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue gathers the searches for galaxies of apparent size greater than 0.1mm (6.7") behind the Milky Way from photographic surveys in the near infrared. The five volumes cover the galactic longitude ranges -7 to +68{deg}, and 210 to 250{deg}.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/33
- Title:
- Gal. midplane Spitzer/IRAC candidate YSOs (SPICY)
- Short Name:
- J/ApJS/254/33
- Date:
- 19 Jan 2022 09:09:49
- Publisher:
- CDS
- Description:
- We present ~120000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l~255{deg} and 110{deg}, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO data sets to take full advantage of Spitzer's spatial resolution and sensitivity in the mid-infrared ~3-9{mu}m range. Multiwavelength color/magnitude distributions provide intuition about how the classifier separates YSOs from other red IRAC sources and validate that the sample is consistent with expectations for disk/envelope-bearing pre-main-sequence stars. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample. Most of the candidates are in regions with mid-IR nebulosity, associated with star-forming clouds, but others appear distributed in the field. Using Gaia DR2 distance estimates, we find groups of YSO candidates associated with the Local Arm, the Sagittarius-Carina Arm, and the Scutum-Centaurus Arm. Candidate YSOs visible to the Zwicky Transient Facility tend to exhibit higher variability amplitudes than randomly selected field stars of the same magnitude, with many high-amplitude variables having light-curve morphologies characteristic of YSOs. Given that no current or planned instruments will significantly exceed IRAC's spatial resolution while possessing its wide-area mapping capabilities, Spitzer-based catalogs such as ours will remain the main resources for mid-infrared YSOs in the Galactic midplane for the near future.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/158
- Title:
- Gas structure comparison; NGC 253 and Milky Way
- Short Name:
- J/ApJ/899/158
- Date:
- 14 Mar 2022 07:10:20
- Publisher:
- CDS
- Description:
- We compare molecular gas properties in the starbursting center of NGC253 and the Milky Way Galactic center (GC) on scales of ~1-100pc using dendrograms and resolution-, area-, and noise-matched data sets in CO(1-0) and CO(3-2). We find that the size-line width relations in NGC253 and the GC have similar slope, but NGC253 has larger line widths by factors of ~2-3. The {sigma}2/R dependency on column density shows that, in the GC, on scales of 10-100pc the kinematics of gas over N>3x1021/cm^2^ are compatible with gravitationally bound structures. In NGC253 this is only the case for column densities N>3x1022/cm^2^. The increased line widths in NGC253 originate in the lower column density gas. This high velocity dispersion, not gravitationally self-bound gas, is likely in transient structures created by the combination of high average densities and feedback in the starburst. The high densities turn the gas molecular throughout the volume of the starburst, and the injection of energy and momentum by feedback significantly increases the velocity dispersion at a given spatial scale over what is observed in the GC.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/89
- Title:
- 1482 Gaussian clumps in the Central Molecular Zone
- Short Name:
- J/ApJ/897/89
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We carry out a systematic study of the density structure of gas in the Central Molecular Zone (CMZ) in the Galactic center by extracting clumps from the APEX Telescope Large Area Survey of the Galaxy survey at 870{mu}m. We find that the clumps follow a scaling of m={rho}_0_r^3^, which corresponds to a characteristic density of n_H_2__=1.6x10^3^/cm^3^ ({rho}_0_=112M{sun}/pc^3^) with a variation of ~0.5dex, where we assumed a gas-to-dust mass ratio of 100. This characteristic density can be interpreted as the result of thermal pressure equilibrium between the molecular gas and the warm ambient interstellar medium. Such an equilibrium can plausibly be established since shear has approximately the same strength as self-gravity. Our findings may explain the fact that star formation in the CMZ is highly inefficient compared to the rest of the Milky Way disk. We also identify a population of clumps whose densities are two orders of magnitudes higher in the vicinity of the Sgr B2 region, which we propose are produced by collisions between the clumps of lower densities. For these collisions to occur, processes such as compressive tides probably have created the appropriate condition by assembling the clumps together.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A14
- Title:
- GaussPy+ decomposition of Galactic Ring Survey
- Short Name:
- J/A+A/633/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of large molecular line surveys of the Galactic plane is essential for our understanding of the gas kinematics on Galactic scales and, in particular, its link with the formation and evolution of dense structures in the interstellar medium. An approximation of the emission peaks with Gaussian functions allows for an efficient and straightforward extraction of useful physical information contained in the shape and Doppler-shifted frequency of the emission lines contained in these enormous data sets. In this work, we present an overview and the first results of a Gaussian decomposition of the entire Galactic Ring Survey (GRS) ^13^CO (1-0) data that consists of about 2.3 million spectra. We performed the decomposition with the fully automated GaussPy+ algorithm and fitted about 4.6 million Gaussian components to the GRS spectra. These decomposition results enable novel and unexplored ways to interpret and study the gas velocity structure. We discuss the statistics of the fit components and relations between the fitted intensities, velocity centroids, and velocity dispersions. We find that the magnitude of the velocity dispersion values increase towards the inner Galaxy and around the Galactic midplane, which we speculate is partly due to the influence of the Galactic bar and regions with higher non-thermal motions located in the midplane, respectively. We also used our decomposition results to infer global properties of the gas emission and find that the number of fit components used per spectrum is indicative of the amount of structure along the line of sight. We find that the emission lines from regions located on the far side of the Galaxy show increased velocity dispersion values, which are likely due to beam averaging effects. We demonstrate how this trend has the potential to aid in characterising Galactic structure by disentangling emission that belongs to the nearby Aquila Rift molecular cloud from emission that is more likely associated with the Perseus and Outer spiral arms. With this work, we also make our entire decomposition results available.
239. GD-1 stellar stream
- ID:
- ivo://CDS.VizieR/J/MNRAS/486/2995
- Title:
- GD-1 stellar stream
- Short Name:
- J/MNRAS/486/2995
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use ESA/Gaia astrometry together with SEGUE and LAMOST measurements of the GD-1 stellar stream to explore the improvement on the Galactic gravitational potential that these new data provide. Assuming a realistic universal model for the dark matter halo together with reasonable models of the baryonic components, we find that the orbital solutions for GD-1 require the circular velocity at the Solar radius to be V_circ_(R_{sun}_)=244+/-4km/s, and also that the density flattening of the dark halo is q_rho_=0.82^+0.25^_-0.13_. The corresponding Galactic mass within 20kpc was estimated to be M_MW_(<20kpc)=2.5+/-0.2x10^11^M_{sun}_. Moreover, Gaia's excellent proper motions also allowed us to constrain the velocity dispersion of the GD-1 stream in the direction tangential to the line of sight to be <2.30km/s (95% confidence limit), confirming the extremely cold dynamical nature of this system.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A102
- Title:
- GES N/O abundance ratio in the Milky Way
- Short Name:
- J/A+A/618/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundance ratio N/O is a useful tool to study the interplay of galactic processes, for example star formation efficiency, timescale of infall, and outflow loading factor. We aim to trace log(N/O) versus [Fe/H] in the Milky Way and to compare this ratio with a set of chemical evolution models to understand the role of infall, outflow, and star formation efficiency in the building up of the Galactic disc. We used the abundances from idr2-3, idr4, idr5 data releases of the Gaia-ESO Survey both for Galactic field and open cluster stars. We determined membership and average composition of open clusters and we separated thin and thick disc field stars. We considered the effect of mixing in the abundance of N in giant stars. We computed a grid of chemical evolution models, suited to reproduce the main features of our Galaxy, exploring the effects of the star formation efficiency, infall timescale, and differential outflow. With our samples, we map the metallicity range -0.6<=[Fe/H]<=0.3 with a corresponding -1.2<=log(N/O)<=-0.2, where the secondary production of N dominates. Thanks to the wide range of Galactocentric distances covered by our samples, we can distinguish the behaviour of log(N/O) in different parts of the Galaxy. Our spatially resolved results allow us to distinguish differences in the evolution of N/O with Galactocentric radius. Comparing the data with our models, we can characterise the radial regions of our Galaxy. A shorter infall timescale is needed in the inner regions, while the outer regions need a longer infall timescale, coupled with a higher star formation efficiency. We compare our results with nebular abundances obtained in MaNGA galaxies, finding in our Galaxy a much wider range of log(N/O) than in integrated observations of external galaxies of similar stellar mass, but similar to the ranges found in studies of individual HII regions.
