- ID:
- ivo://CDS.VizieR/J/ApJ/802/127
- Title:
- PHAT stellar cluster survey. II. AP catalog
- Short Name:
- J/ApJ/802/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a stellar cluster catalog for the Panchromatic Hubble Andromeda Treasury (PHAT) survey using image classifications collected from the Andromeda Project (AP) citizen science website. We identify 2753 clusters and 2270 background galaxies within ~0.5deg^2^ of PHAT imaging searched, or ~400kpc^2^ in deprojected area at the distance of the Andromeda Galaxy (M31). These identifications result from 1.82million classifications of ~20000 individual images (totaling ~7gigapixels) by tens of thousands of volunteers. We show that our crowd-sourced approach, which collects >80 classifications per image, provides a robust, repeatable method of cluster identification. The high spatial resolution Hubble Space Telescope images resolve individual stars in each cluster and are instrumental in the factor of ~6 increase in the number of clusters known within the survey footprint. We measure integrated photometry in six filter passbands, ranging from the near-UV to the near-IR. PHAT clusters span a range of ~8 magnitudes in F475W (g-band) luminosity, equivalent to ~4 decades in cluster mass. We perform catalog completeness analysis using >3000 synthetic cluster simulations to determine robust detection limits and demonstrate that the catalog is 50% complete down to ~500M_{sun}_ for ages <100Myr. We include catalogs of clusters, background galaxies, remaining unselected candidates, and synthetic cluster simulations, making all information publicly available to the community. The catalog published here serves as the definitive base data product for PHAT cluster science, providing a census of star clusters in an L^*^ spiral galaxy with unmatched sensitivity and quality.
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- ID:
- ivo://CDS.VizieR/J/ApJ/752/95
- Title:
- PHAT stellar cluster survey. I. Year 1
- Short Name:
- J/ApJ/752/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an ongoing Hubble Space Telescope (HST) multi-cycle program to obtain high spatial resolution imaging of one-third of the M31 disk at ultraviolet through near-infrared wavelengths. In this paper, we present the first installment of the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will be among the largest and most comprehensive surveys of resolved star clusters in any galaxy. The exquisite spatial resolution achieved with HST has allowed us to identify hundreds of new clusters that were previously inaccessible with existing ground-based surveys. We identify 601 clusters in the Year 1 sample, representing more than a factor of four increase over previous catalogs within the current survey area (390 arcmin^2^). This work presents results derived from the first ~25% of the survey data; we estimate that the final sample will include ~2500 clusters. For the Year 1 objects, we present a catalog with positions, radii, and six-band integrated photometry. Along with a general characterization of the cluster luminosities and colors, we discuss the cluster luminosity function, the cluster size distributions, and highlight a number of individually interesting clusters found in the Year 1 search.
- ID:
- ivo://CDS.VizieR/J/AJ/89/1707
- Title:
- Photographic observations of variable stars in M9
- Short Name:
- J/AJ/89/1707
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New observations from the southern hemisphere have been used to check the periods for the 11 RR Lyrae variables in and around the globular cluster Messier 9. The periods were determined previously with data from northern observatories where M9 can only be observed over a small range in hour angle. Three of the eleven published periods were found to be in error. As a result of this, the mean period of the RRc variables has been revised from 0.279d to 0.341d, the mean period of the RRab variables has been revised from 0.614d to 0.621d,and a star previously believed to be an RR Lyrae has been reclassified as a Population II Cepheid. One of the RRc variables may be a double-mode pulsator. Another variable was studied, but the data were not sufficient for determining its period.
- ID:
- ivo://CDS.VizieR/J/ApJS/191/389
- Title:
- Photometric monitoring in {sigma} Ori cluster
- Short Name:
- J/ApJS/191/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-precision photometry on 107 variable low-mass stars and brown dwarfs in the ~3Myr {sigma} Orionis open cluster. We have carried out I-band photometric monitoring within two fields, encompassing 153 confirmed or candidate members of the low-mass cluster population, from 0.02 to 0.5M_{sun}_. We are sensitive to brightness changes on timescales from 10 minutes to two weeks with amplitudes as low as 0.004mag, and find variability on these timescales in nearly 70% of cluster members. We identify both periodic and aperiodic modes of variability, as well as semi-periodic rapid fading events that are not accounted for by the standard explanations of rotational modulation of surface features or accretion. We have incorporated both optical and infrared color data to uncover trends in variability with mass and circumstellar disks.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/1633
- Title:
- Photometric study of globular clusters
- Short Name:
- J/MNRAS/475/1633
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we describe the photometric and spectroscopic properties of multiple populations in seven northern globular clusters. In this study, we employ precise ground-based photometry from the private collection of Stetson, space photometry from the Hubble Space Telescope (HST), literature abundances of Na and O, and Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey abundances for Mg, Al, C, and N. Multiple populations are identified by their position in the C_U,B,I_-V pseudo colour-magnitude diagram (pseudo-CMD) and confirmed with their chemical composition determined using abundances. We confirm the expectation from previous studies that the red giant branches (RGBs) in all seven clusters are split and the different branches have different chemical compositions. The Mg-Al anticorrelations were well explored by the APOGEE and Gaia-ESO surveys for most globular clusters, some clusters showing bimodal distributions, while others continuous distributions. Even though the structure (i.e. bimodal versus continuous) of Mg-Al can greatly vary, the Al-rich and Al-poor populations do not seem to have very different photometric properties, agreeing with theoretical calculations. There is no one-to-one correspondence between the Mg-Al anticorrelation shape (bimodal versus continuous) and the structure of the RGB seen in the HST pseudo-CMDs, with the HSTphotometric information usually implying more complex formation/evolution histories than the spectroscopic ones. We report on finding two second-generation horizontal branch (HB) stars in M5, and five second-generation asymptotic giant branch (AGB) stars in M92, which is the most metal-poor cluster to date in which second-generation AGB stars have been observed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/3044
- Title:
- Photometry and abundances of NGC1851 stars
- Short Name:
- J/MNRAS/442/3044
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 1851 is surrounded by a stellar component that extends more than 10 times beyond the tidal radius. Although the nature of this stellar structure is not known, it has been suggested to be a sparse halo of stars or associated with a stellar stream. We analyse the nature of this intriguing stellar component surrounding NGC 1851 by investigating its radial velocities and chemical composition, in particular in comparison with those of the central cluster analysed in a homogeneous manner. In total we observed 23 stars in the halo with radial velocities consistent with NGC 1851, and for 15 of them we infer [Fe/H] abundances. Our results show that (i) stars dynamically linked to NGC 1851 are present at least up to ~2.5 tidal radii, supporting the presence of a halo of stars surrounding the cluster; (ii) apart from the NGC 1851 radial velocity-like stars, our observed velocity distribution agrees with that expected from Galactic models, suggesting that no other substructure (such as a stream) at different radial velocities is present in our field; (iii) the chemical abundances for the s-process elements Sr and Ba are consistent with the s-normal stars observed in NGC 1851; (iv) all halo stars have metallicities, and abundances for the other studied elements Ca, Mg and Cr, consistent with those exhibited by the cluster. The complexity of the whole NGC 1851 cluster+halo system may agree with the scenario of a tidally disrupted dwarf galaxy in which NGC 1851 was originally embedded.
- ID:
- ivo://CDS.VizieR/J/AJ/101/1699
- Title:
- Photometry in globular cluster NGC 6229
- Short Name:
- J/AJ/101/1699
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD-based BV photometry for over 1100 stars in and around the globular cluster NGC 6229. For the first time, the cluster's entire giant branch and its horizontal branch are delineated, from which metallicity ([Fe/H]~-1.4) and distance (d__{sun}_~28kpc; d_GC_~27kpc) estimates ensue. NGC 6229 is found to have a relatively blue horizontal branch for its intermediate metallicity, which is unusual for an outer halo cluster. Its low R value (defined as N_HB_/N_RG_) hints that the blue color of its horizontal branch is due to a lower than average helium abundance. Three possible new variable stars are identified, including one RR Lyrae and two long-period variables. We present a brief review of our knowledge of basic data for the 13 globular clusters lying more than 24 kpc from the Galactic center. The unusually red horizontal branch phenomenon is common only among the outermost clusters. An average R value for these clusters suggests the effect is not caused by an overabundance of helium. The Oosterhoff dichotomy apparently persists into the outer halo, although the number of clusters with RR Lyrae variables is small.
- ID:
- ivo://CDS.VizieR/J/AJ/148/27
- Title:
- Photometry in globular clusters. I. NGC 1851
- Short Name:
- J/AJ/148/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of multiple populations (MPs) in globular clusters (GCs) has become a forefront area of research in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been observed photometrically in many GCs, while broad abundance distributions of certain elements have been detected spectroscopically in most, if not all, GCs. UV photometry has been crucial in discovering and analyzing these MPs, but the Johnson U and the Stromgren and Sloan u filters that have generally been used are relatively inefficient and very sensitive to reddening and atmospheric extinction. In contrast, the Washington C filter is much broader and redder than these competing UV filters, making it far more efficient at detecting MPs and much less sensitive to reddening and extinction. Here, we investigate the use of the Washington system to uncover MPs using only a 1 m telescope. Our analysis of the well-studied GC NGC 1851 finds that the C filter is both very efficient and effective at detecting its previously discovered MPs in the RGB and SGB. Remarkably, we have also detected an intrinsically broad MS best characterized by two distinct but heavily overlapping populations that cannot be explained by binaries, field stars, or photometric errors. The MS distribution is in very good agreement with that seen on the RGB, with ~30% of the stars belonging to the second population. There is also evidence for two sequences in the red horizontal branch, but this appears to be unrelated to the MPs in this cluster. Neither of these latter phenomena have been observed previously in this cluster. The redder MS stars are also more centrally concentrated than the blue MS. This is the first time MPs in an MS have been discovered from the ground, and using only a 1 m telescope. The Washington system thus proves to be a very powerful tool for investigating MPs, and holds particular promise for extragalactic objects where photons are limited.
- ID:
- ivo://CDS.VizieR/J/AJ/64/28
- Title:
- Photometry in the globular cluster M22
- Short Name:
- J/AJ/64/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photovisual and photographic magnitudes of more than 400 stars in the globular cluster M22 have been measured. The resulting color-magnitude diagram extends to slightly fainter than the RR Lyurae domain and is generally similar to those for other globular clusters, in particular most resembling the diagram for M13
- ID:
- ivo://CDS.VizieR/J/A+A/525/A19
- Title:
- Photometry of globulars in early galaxies
- Short Name:
- J/A+A/525/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The combination of optical and near-infrared (NIR) colours has the potential to break the age/metallicity degeneracy and offers a better metallicity sensitivity than optical colours alone. Previous studies of extragalactic globular clusters (GCs) with this colour combination, however, have suffered from small samples or have been restricted to a few galaxies. We compile a homogeneous and representative sample of GC systems with multi-band photometry to be used in subsequent papers where ages and metallicity distributions will be studied.
