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2071. HST UBVI photometry of NGC 3081 inner regions
ID:
ivo://CDS.VizieR/J/AJ/127/1982
Title:
HST UBVI photometry of NGC 3081 inner regions
Short Name:
J/AJ/127/1982
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Hubble Space Telescope Wide Field Planetary Camera 2 images of the inner regions of NGC 3081, an absolute magnitude M_B_=-20.0 early-type barred spiral having four well-defined resonance rings: a nuclear ring, an inner ring, an outer R_1_ ring, and an outer R'_2_ pseudoring. Here we focus on a photometric study of the inner ring, a feature likely associated with an inner 4:1 resonance near the ends of the bar. The ring is notable for its high contrast and sharp definition, which is due to a significant degree of active star formation. The ring is also notable for its significant intrinsic elongation and parallel alignment with the bar.
2072. HST UVI photometry of M15. II.
ID:
ivo://CDS.VizieR/J/AJ/107/1745
Title:
HST UVI photometry of M15. II.
Short Name:
J/AJ/107/1745
Date:
21 Oct 2021
Publisher:
CDS
Description:
The projected density distribution of resolved stars near the center of M15 is shown to be consistent with either a power-law cusp N(r) ~ r^{alpha}^, with {alpha} ~ -0.85+/-0.2, or with a King model with a core of radius <~ 2" (best fit r(core)=1.3"). The inferred slope is in agreement with the theoretical value, {alpha}=-0.75, calculated by Bahcall and Wolf for the distribution of equal-mass stars surrounding a massive black hole and is also consistent with the radial profile expected from core collapse without a central black hole. The object AC 214 is a candidate for the central density cusp. Analysis of Monte Carlo simulations of the diffuse light indicates that, using current analysis techniques and available data, the residual light is not a reliable indicator of the true density distribution. This is contrary to earlier work. Photometric measurements in V and I of more than 5x10^3^ stars (and in U, V, and I of >~1500 stars) are used to construct color-magnitude diagrams in the central 1' of M15. Fourteen blue straggler candidates are identified in the inner 20". The central color gradient noticed by previous researchers is caused by a central depletion of bright red giant stars rather than an excess of blue stragglers or blue horizontal branch stars.
2073. HST UV-IR photometry in CLASH galaxy clusters
ID:
ivo://CDS.VizieR/J/ApJ/848/37
Title:
HST UV-IR photometry in CLASH galaxy clusters
Short Name:
J/ApJ/848/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new method for photometering objects in galaxy clusters. We introduce a mode-filtering technique for removing spatially variable backgrounds, improving both detection and photometric accuracy (roughly halving the scatter in the red sequence compared to previous catalogs of the same clusters). This method is based on robustly determining the distribution of background pixel values and should provide comparable improvement in photometric analysis of any crowded fields. We produce new multiwavelength catalogs for the 25 CLASH cluster fields in all 16 bandpasses from the UV through the near-IR, as well as rest-frame magnitudes. A comparison with spectroscopic values from the literature finds a ~30% decrease in the redshift deviation from previously released CLASH photometry. This improvement in redshift precision, in combination with a detection scheme designed to maximize purity, yields a substantial upgrade in cluster member identification over the previous CLASH galaxy catalog. We construct luminosity functions for each cluster, reliably reaching depths of at least 4.5mag below M* in every case, and deeper still in several clusters. We measure M* , {alpha}, and their redshift evolution, assuming the cluster populations are coeval, and find little to no evolution of {alpha}{<~}-0.9<~{alpha}{<~}-0.8, and M* values consistent with passive evolution. We present a catalog of galaxy photometry, photometric and spectroscopic redshifts, and rest-frame photometry for the full fields of view of all 25 CLASH clusters. Not only will our new photometric catalogs enable new studies of the properties of CLASH clusters, but mode-filtering techniques, such as those presented here, should greatly enhance the data quality of future photometric surveys of crowded fields.
2074. HST UV,V,I photometry of NGC7673 star clusters
ID:
ivo://CDS.VizieR/J/A+A/391/857
Title:
HST UV,V,I photometry of NGC7673 star clusters
Short Name:
J/A+A/391/857
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the star cluster system in the starburst galaxy NGC 7673 using archival Hubble Space Telescope WFPC2 broad-band images. For the first time we are able to examine the internal structures of the prominent optical clumps in this galaxy. The clumps are composed of young stars, 16-33% of which are in bright star clusters. We identify 268 star cluster candidates in both the F555W and F814W images, and 50 clusters with the F255W filter. These data allow us to estimate ages and masses using color-magnitude and two-color diagrams for our sample. We find a population of young, <6Myr clusters located throughout the galaxy with concentrations in the clumps. Star cluster mass estimates are 5-50x10^4^M_{sun}_ for the brightest objects. The starburst remains active in physically well-separated regions, indicating a widespread starburst trigger. We discuss clump lifetimes, their implications for the future evolution of NGC 7673, and possible relationships to high redshift starbursts.
2075. HST view of YSOs in the LMC
ID:
ivo://CDS.VizieR/J/ApJ/707/1417
Title:
HST view of YSOs in the LMC
Short Name:
J/ApJ/707/1417
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used archival Hubble Space Telecope (HST) H{alpha} images to study the immediate environments of massive and intermediate-mass young stellar object (YSO) candidates in the Large Magellanic Cloud (LMC). The sample of YSO candidates, taken from Gruendl & Chu (2009, Cat. J/ApJS/184/172), was selected based on Spitzer IRAC and MIPS observations of the entire LMC and complementary ground-based optical and near-infrared observations. We found HST H{alpha} images for 99 YSO candidates in the LMC, of which 82 appear to be genuine YSOs. More than 95% of the YSOs are found to be associated with molecular clouds. YSOs are seen in three different kinds of environments in the H{alpha} images: in dark clouds, inside or on the tip of bright-rimmed dust pillars, and in small HII regions. Comparisons of spectral energy distributions for YSOs in these three different kinds of environments suggest that YSOs in dark clouds are the youngest, YSOs with small HII regions are the most evolved, and YSOs in bright-rimmed dust pillars span a range of intermediate evolutionary stages. This rough evolutionary sequence is substantiated by the presence of silicate absorption features in the Spitzer Infrared Spectrograph spectra of some YSOs in dark clouds and in bright-rimmed dust pillars, but not those of YSOs in small HII regions. We present a discussion on triggered star formation for YSOs in bright-rimmed dust pillars or in dark clouds adjacent to HII regions. As many as 50% of the YSOs are resolved into multiple sources in high-resolution HST images.
2076. HST VI photometry and proper motions in NGC 6528
ID:
ivo://CDS.VizieR/J/A+A/385/67
Title:
HST VI photometry and proper motions in NGC 6528
Short Name:
J/A+A/385/67
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using two epochs of HST/WFPC2 images of the metal-rich globular cluster NGC 6528 we derive the proper motions of the stars and use them to separate the stars belonging to NGC 6528 from those of the Galactic bulge. The stellar sequences in the resulting colour-magnitude diagram for the cluster are significantly better determined than in previously published data. From comparison of the colour-magnitude diagram with the fiducial line for NGC 6553 from Zoccali et al. (2001AJ....121.2638Z) we conclude that the two globular clusters have the same age. Further, using alpha-enhanced stellar isochrones, NGC 6528 is found to have an age of 11+/-2Gyr. This fitting of isochrones also give that the cluster is 7.2kpc away from us. From the measured velocities both the proper motion of the cluster and the velocity dispersion in the Galactic bulge are found. NGC 6528 is found to have a proper motion relative to the Galactic bulge of <mu_l_>=0.006 and <mu_b_>=0.044 arcsec per century. Using stars with 14<V_555_<19 (i.e. the red giant branch and horizontal branch) we find, for the Galactic bulge, sigma_l_=0.33+/-0.03 and sigma_b_=0.25+/-0.02 arcsec per century. This give sigma_l/sigma_b=1.32+/-0.16, consistent both with previous proper motion studies of K giants in the Galactic bulge as well as with predictions by models of the kinematics of bulge stars.
2077. HST VI photometry of Bol 514 in M31
ID:
ivo://CDS.VizieR/J/A+A/473/429
Title:
HST VI photometry of Bol 514 in M31
Short Name:
J/A+A/473/429
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the density profile of the remote M 31 globular cluster B514, obtained from HST/ACS observations.
2078. HST VI photometry of HD 97950 cluster members stars
ID:
ivo://CDS.VizieR/J/ApJ/764/73
Title:
HST VI photometry of HD 97950 cluster members stars
Short Name:
J/ApJ/764/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present deep Hubble Space Telescope/Wide Field and Planetary Camera 2 photometry of the young HD 97950 star cluster in the giant H II region NGC 3603. The data were obtained in 1997 and 2007 permitting us to derive membership based on proper motions of the stars. Our data are consistent with an age of 1 Myr for the HD 97950 cluster. A possible age spread, if present in the cluster, appears to be small. The global slope of the incompleteness-corrected mass function for member stars within 60" is {Gamma}=-0.88+/-0.15, which is flatter than the value of a Salpeter slope of -1.35. The radially varying mass function shows pronounced mass segregation ranging from slopes of -0.26 +/-0.32 in the inner 5" to -0.94+/-0.36 in the outermost annulus (40"-60"). Stars more massive than 50M_{sun}_ are found only in the cluster center. The {Lambda} minimum spanning tree technique confirms significant mass segregation down to 30M_{sun}_. The dependence of {Lambda} on mass, i.e., that high-mass stars are more segregated than low-mass stars, and the (weak) dependence of the velocity dispersion on stellar mass might imply that the mass segregation is dynamical in origin. While primordial segregation cannot be excluded, the properties of the mass segregation indicate that dynamical mass segregation may have been the dominant process for segregation of high-mass stars.
2079. HST VI photometry of variable stars in Leo T
ID:
ivo://CDS.VizieR/J/ApJ/756/108
Title:
HST VI photometry of variable stars in Leo T
Short Name:
J/ApJ/756/108
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from the first combined study of variable stars and star formation history (SFH) of the Milky Way "ultra-faint" dwarf (UFD) galaxy Leo T, based on F606W and F814W multi-epoch archive observations obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. We have detected 14 variable stars in the galaxy. They include one fundamental-mode RR Lyrae star and 11 Anomalous Cepheids with periods shorter than 1 day, thus suggesting the occurrence of multiple star formation episodes in this UFD, of which one about 10 Gyr ago produced the RR Lyrae star. A new estimate of the distance to Leo T of 409^+29^_-27_kpc (distance modulus of 23.06+/-0.15mag) was derived from the galaxy's RR Lyrae star. Our V, V-I color-magnitude diagram (CMD) of Leo T reaches V~29mag and shows features typical of a galaxy in transition between dwarf irregular and dwarf spheroidal types. A quantitative analysis of the SFH, based on the comparison of the observed V, V-I CMD with the expected distribution of stars for different evolutionary scenarios, confirms that Leo T has a complex SFH dominated by two enhanced periods about 1.5 and 9 Gyr ago, respectively. The distribution of stars and gas shows that the galaxy has a fairly asymmetric structure.
2080. HST VI stars in Shapley Constellation III
ID:
ivo://CDS.VizieR/J/ApJ/738/137
Title:
HST VI stars in Shapley Constellation III
Short Name:
J/ApJ/738/137
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope Wide-Field Planetary Camera 2. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double-Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63, and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.