- ID:
- ivo://CDS.VizieR/J/ApJ/811/30
- Title:
- Machine learning metallicity predictions using SDSS
- Short Name:
- J/ApJ/811/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extremely metal-poor (EMP) stars ([Fe/H]<=-3.0dex) provide a unique window into understanding the first generation of stars and early chemical enrichment of the universe. EMP stars are exceptionally rare, however, and the relatively small number of confirmed discoveries limits our ability to exploit these near-field probes of the first ~500Myr after the Big Bang. Here, a new method to photometrically estimate [Fe/H] from only broadband photometric colors is presented. I show that the method, which utilizes machine-learning algorithms and a training set of ~170000 stars with spectroscopically measured [Fe/H], produces a typical scatter of ~0.29dex. This performance is similar to what is achievable via low-resolution spectroscopy, and outperforms other photometric techniques, while also being more general. I further show that a slight alteration to the model, wherein synthetic EMP stars are added to the training set, yields the robust identification of EMP candidates. In particular, this synthetic-oversampling method recovers ~20% of the EMP stars in the training set, at a precision of ~0.05. Furthermore, ~65% of the false positives from the model are very metal-poor stars ([Fe/H]<=-2.0dex). The synthetic-oversampling method is biased toward the discovery of warm (~F-type) stars, a consequence of the targeting bias from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding survey. This EMP selection method represents a significant improvement over alternative broadband optical selection techniques. The models are applied to >12 million stars, with an expected yield of ~600 new EMP stars, which promises to open new avenues for exploring the early universe.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/130/734
- Title:
- Magnetic white dwarfs from SDSS DR2 and DR3
- Short Name:
- J/AJ/130/734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fifty-two magnetic white dwarfs have been identified in spectroscopic observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002 and the end of 2004, including Data Releases 2 and 3. Although not as numerous or diverse as the discoveries from the first data release, the collection exhibits polar field strengths ranging from 1.5 to ~1000MG and includes two new unusual atomic DQA examples, a molecular DQ, and five stars that show hydrogen in fields above 500MG. The highest field example, SDSS J2346+3853, may be the most strongly magnetic white dwarf yet discovered. Analysis of the photometric data indicates that the magnetic sample spans the same temperature range as for non-magnetic white dwarfs from the SDSS, and support is found for previous claims that magnetic white dwarfs tend to have larger masses than their non-magnetic counterparts. A glaring exception to this trend is the apparently low-gravity object SDSS J0933+1022, which may have a history involving a close binary companion.
313. MaNGA catalog, DR15
- ID:
- ivo://CDS.VizieR/J/AJ/154/86
- Title:
- MaNGA catalog, DR15
- Short Name:
- J/AJ/154/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing signal-to-noise ratio, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on i-band absolute magnitude (M_i_), or, for a small subset of our sample, M i and color (NUV-i). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to M_i_ and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (Re), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range 5x10^8^<=M*<=3x10^11^M_{sun}/h^2^ and are sampled at median physical resolutions of 1.37 and 2.5kpc for the Primary and Secondary samples, respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume-limited sample.
- ID:
- ivo://CDS.VizieR/J/A+A/570/A82
- Title:
- Mapping accretion variability in NGC 2264
- Short Name:
- J/A+A/570/A82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our study aims at characterizing the accretion properties of several hundred members of the star-forming region NGC 2264 (3Myr). We performed a deep u,g,r,i mapping of the cluster with CFHT/MegaCam, and monitored the simultaneous u+r variability of its members over a baseline of two weeks. Stellar parameters are determined homogeneously for about 750 monitored young objects, 40% of which are accreting T Tauri stars. Accretion properties and accretion variability are investigated and characterized from UV excess measurements. Non-accreting members of the cluster define the reference UV emission level over which flux excess is detected and measured.
- ID:
- ivo://CDS.VizieR/J/MNRAS/383/1513
- Title:
- 2MASS, SDSS and FIRST fluxes of QSOs
- Short Name:
- J/MNRAS/383/1513
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Starting from a sample of Sloan Digital Sky Survey quasars appearing also in the Two-Micron All-Sky Survey, we study the continuum properties of ~1000 objects observed in eight bands, from near-infrared to ultraviolet. We construct the mean spectral energy distribution (SED) and compare and contrast the continua of radio-loud and radio-quiet quasar (RLQ and RQQ, respectively) objects. The SEDs of the two populations are significantly different, in the sense that RLQs are redder with power-law spectral indices <alpha_RLQ_>=0.55+/-0.04 and <alpha_RQQ_>=0.31+/-0.01 in the spectral range between 10^14.5^ and 10^15.35^Hz. This difference is discussed in terms of different extinctions, different disc temperatures, or slopes of the non-thermal component.
- ID:
- ivo://CDS.VizieR/J/MNRAS/404/1817
- Title:
- 2MASS/SDSS data for 806 ultracool dwarfs
- Short Name:
- J/MNRAS/404/1817
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify 806 ultracool dwarfs (of which 34 are newly discovered L dwarfs) from their Sloan Digital Sky Survey (SDSS) riz photometry and obtain proper motions through cross-matching with the United Kingdom Infrared Telescope Infrared Deep Sky Survey (UKIDSS) and Two-Micron All-Sky Survey (2MASS). Proper-motion and distance constraints show that nine of our ultracool dwarfs are members of widely separated binary systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/239
- Title:
- MaxBCG catalog of 13823 galaxy clusters from SDSS
- Short Name:
- J/ApJ/660/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of galaxy clusters selected using the maxBCG red-sequence method from Sloan Digital Sky Survey photometric data. This catalog includes 13823 clusters with velocity dispersions greater than ~400km/s and is the largest galaxy cluster catalog assembled to date. They are selected in an approximately volume-limited way from a 0.5Gpc^3^ region covering 7500deg^2^ of sky between redshifts 0.1 and 0.3. Each cluster contains between 10 and 190 E/S0 ridgeline galaxies brighter than 0.4L* within a scaled radius R_200_.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/143
- Title:
- MC2: redshift analysis of CIZA J2242.8+5301
- Short Name:
- J/ApJ/805/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray and radio observations of CIZA J2242.8+5301 suggest that it is a major cluster merger. Despite being well studied in the X-ray and radio, little has been presented on the cluster structure and dynamics inferred from its galaxy population. We carried out a deep (i<25) broadband imaging survey of the system with Subaru SuprimeCam (g and i bands) and the Canada-France-Hawaii Telescope (r band), as well as a comprehensive spectroscopic survey of the cluster area (505 redshifts) using Keck DEep Imaging Multi-Object Spectrograph. We use these data to perform a comprehensive galaxy/redshift analysis of the system, which is the first step to a proper understanding of the geometry and dynamics of the merger, as well as using the merger to constrain self-interacting dark matter. We find that the system is dominated by two subclusters of comparable richness with a projected separation of 6.9'_-0.5_^+0.7^ (1.3_-0.10_^+0.13^Mpc). We find that the north and south subclusters have similar redshifts of z~0.188 with a relative line-of-sight (LOS) velocity difference of 69+/-190km/s. We also find that north and south subclusters have velocity dispersions of 1160_-90_^+100^ and 1080_-70_^+100^km/s, respectively. These correspond to masses of 16.1_-3.3_^+4.6^x10^14^ and 13.0_-2.5_^+4.0^x10^14^M_{Sun}_, respectively. While velocity dispersion measurements of merging clusters can be biased, we believe the bias in this system to be minor due to the large projected separation and nearly plane-of-sky merger configuration. We also find that the cDs of the north and south subclusters are very near their subcluster centers, in both projection (55 and 85kpc, respectively) and normalized LOS velocity (|{Delta}v|/{sigma}_v_=0.43+/-0.13 and 0.21+/-0.12 for the north and south, respectively). CIZA J2242.8+5301 is a relatively clean dissociative cluster merger with near 1:1 mass ratio, which makes it an ideal merger for studying merger-associated physical phenomena.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/65
- Title:
- MegaCam survey of outer halo satellites. I.
- Short Name:
- J/ApJ/860/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a deep, systematic imaging study of satellites in the outer halo of the Milky Way. Our sample consists of 58 stellar overdensities --i.e., substructures classified as either globular clusters, classical dwarf galaxies, or ultra-faint dwarf galaxies-that are located at Galactocentric distances of R_GC_>=25kpc (outer halo) and out to ~400kpc. This includes 44 objects for which we have acquired deep, wide-field, g- and r-band imaging with the MegaCam mosaic cameras on the 3.6m Canada-France-Hawaii Telescope and the 6.5m Magellan-Clay telescope. These data are supplemented by archival imaging, or published gr photometry, for an additional 14 objects, most of which were discovered recently in the Dark Energy Survey (DES). We describe the scientific motivation for our survey, including sample selection, observing strategy, data reduction pipeline, calibration procedures, and the depth and precision of the photometry. The typical 5{sigma} point-source limiting magnitudes for our MegaCam imaging-which collectively covers an area of ~52deg^2^ --are g_lim_~25.6 and r_lim_~25.3 AB mag. These limits are comparable to those from the coadded DES images and are roughly a half-magnitude deeper than will be reached in a single visit with the Large Synoptic Survey Telescope. Our photometric catalog thus provides the deepest and most uniform photometric database of Milky Way satellites available for the foreseeable future. In other papers in this series, we have used these data to explore the blue straggler populations in these objects, their density distributions, star formation histories, scaling relations, and possible foreground structures.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/13
- Title:
- Member stars of the GD-1 tidal stream
- Short Name:
- J/ApJ/877/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the photometric data from the SDSS survey, the spectroscopic data from the SDSS/SEGUE and the LAMOST surveys, and the astrometric data from the Gaia DR2, we have identified 67 highly probable member stars of the GD-1 cold stellar stream spread along almost its entire length (i.e., from 126{deg} to 203{deg} in R.A.). With the accurate spectroscopic (i.e., metallicity and line-of-sight velocity) and astrometric (i.e., proper motions) information, the position-velocity diagrams, i.e., {phi}_1_-{mu}_{alpha}_, {phi}_1_-{mu}_{delta}_, and {phi}_1_-v_gsr_, of the GD-1 stream are well mapped. The stream has an average metallicity [Fe/H]=-1.96. The rich information of member stars of the stream now available allow one not only to model its origin, but also to place strong constraints on the mass distribution and the gravitational potential of the Milky Way.
