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2741. HST photometry in six M31 globular clusters
ID:
ivo://CDS.VizieR/J/A+A/531/A155
Title:
HST photometry in six M31 globular clusters
Short Name:
J/A+A/531/A155
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present deep (V~28.0) BV photometry obtained with the wide field channel of the Advanced Camera for Surveys on board HST for four M31 globular clusters that were identified as candidate intermediate-age (age~1-9Gyr) by various authors, based on their integrated spectra and/or broad/intermediate-band colors. Two of them (B292 and B350) display an obvious blue horizontal branch, indicating that they are as old as the oldest Galactic globulars. On the other hand, for the other two (B058 and B337), which display red horizontal branches, it was not possible either to confirm or disconfirm the age estimate from integrated spectra. The analysis of the distribution in the spectral indices Mg2 and H{beta} of the M31 and Milky Way clusters whose horizontal branch can be classified as red or blue based on existing CMDs, strongly suggests that classical age diagnostics from integrated spectra may be significantly influenced by the HB morphology of the clusters and can lead to erroneous age-classifications. We also provide the CMD for another two clusters that fall into the field of the main targets, B336, an old and metal-poor globular with a significant population of RR-Lyrae variables, and the newly discovered B531, a cluster with a very red red giant branch.
2742. HST photometry in the wing of the SMC
ID:
ivo://CDS.VizieR/J/AJ/130/1083
Title:
HST photometry in the wing of the SMC
Short Name:
J/AJ/130/1083
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope to image a star field in the wing of the Small Magellanic Cloud (SMC), near the HII region N81. The images were taken in the F336W, F547M, F675W, and F814W filters. From photometry of stars in this field, we construct color-magnitude diagrams (CMDs) for about 4200 stars and compare them with theoretical isochrones.
2743. HST photometry of brightest stars of NGC 588
ID:
ivo://CDS.VizieR/J/A+A/426/399
Title:
HST photometry of brightest stars of NGC 588
Short Name:
J/A+A/426/399
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a double analysis of the ionizing cluster in NGC 588, a giant HII region (GHR) in the outskirts of the nearby galaxy M33. For this purpose, we obtained ground based long-slit spectroscopy and combined it with archival ground based and space borne imaging and spectroscopy, in the wavelength range 1100-9800{AA}. A first modeling of the cluster was performed using integrated properties, such as the spectral energy distribution (SED), broad band colors, nebular emission H{beta} equivalent width, the main ultraviolet resonance lines, and the presence of Wolf-Rayet star features. By applying standard assumptions about the initial mass function (IMF), we were unable to fit satisfactorily these observational data. This contradictory result led us to carry out a second modeling, based on a resolved photometric analysis of individual stars in Hubble Space Telescope (HST) images, by means of finding the best fit isochrone in color-magnitude diagrams (CMD), and assigning a theoretical SED to each individual star. The overall SED of the cluster, obtained by integrating the individual stellar SEDs, is found to fit better the observed SED than the best solution found through the integrated first analysis, but at a significantly later stage of evolution of the cluster of 4.2Myr, as obtained from the best fit to the CMD. A comparative analysis of both methods traces the different results to the effects of statistical fluctuations in the upper end of the IMF, which are significant in NGC 588, with a computed cluster mass of 5600M_{sun}_, as predicted by Cervino et al. (2002A&A...381...51C). We discuss the results in terms of the strong influence of the few most massive stars, six in the case of NGC 588, that dominate the overall SED and, in particular, the ionizing far ultraviolet range beyond the Lyman limit.
2744. HST photometry of Cepheid candidates in M101
ID:
ivo://CDS.VizieR/J/ApJ/777/79
Title:
HST photometry of Cepheid candidates in M101
Short Name:
J/ApJ/777/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
The impact of metallicity on the Cepheid period-luminosity (P-L) relation is investigated using Hubble Space Telescope Advanced Camera for Surveys V and I images of M101. Variations in the reddening-free Wesenheit parameter (W), which is employed as a proxy for luminosity, are examined as a function of the radial distance from the center of M101 (and thus metallicity). We determine that there is no dependence of the slope on metallicity. However, the intercept is found to depend on metallicity by {gamma}_VI_=-0.33+/-0.12mag.dex^-1^ and {gamma}_VI_=-0.71+/-0.17mag.dex^-1^ using 2{sigma} and 3{sigma} rejection criteria, respectively. Sigma-clipping impacts the derived metallicity dependence, and the 2{sigma} criterion applied likely mitigates blending, particularly in the crowded inner regions of M101. A metallicity-corrected distance for M101 is obtained from 619 Cepheids ({mu}=28.96+/-0.11), a result that agrees with the recently determined SN Ia distance. The metallicity effects described can be bypassed by working at near and mid-infrared wavelengths (e.g., the Carnegie Hubble Program).
2745. HST photometry of ESO 338-IG04 globular clusters
ID:
ivo://CDS.VizieR/J/A+A/335/85
Title:
HST photometry of ESO 338-IG04 globular clusters
Short Name:
J/A+A/335/85
Date:
21 Oct 2021
Publisher:
CDS
Description:
Multicolour images of the starbursting metal poor blue compact galaxy ESO 338-IG04 have been obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In the images we find numerous point-like sources concentrated towards the main body of the galaxy, which we identify as globular cluster candidates. We show that these objects are physically associated with the galaxy and that they are spatially extended. Given their high intrinsic luminosities, these objects cannot be individual stars. Using photometric evolution models we show that the objects constitute a rich population of massive star clusters with ages ranging from a few Myr to 10Gyr, and masses ranging from 10^4^ to more than 10^7^M_{sun}_. There are peaks in the age distribution of the clusters: one with objects <=30Myr, one at ~100Myr, one at ~600Myr, one to two at 2.5-5Gyr and one at ~10Gyr. The youngest objects are predominantly found in the crowded starburst region. They have properties which agree with what is expected for young globular clusters, although it cannot be excluded that some of them may be dissolved or disrupted. For objects older than a few times 10Myr, the only plausible explanation is that these are globular clusters. The galaxy presently appears to be involved in a merger, which is the probable cause of the present globular cluster formation. The presence of a numerous intermediate age (2.5 to 5Gyr) population of globular clusters, suggests that a previous merger might have occurred. As the starburst fades, this galaxy will become very rich in globular clusters. Transforming all objects to an age comparable to that of Milky Way globular clusters reveals a luminosity function similar to the Galactic. We suggest that this galaxy is the result of a merger between a dwarf elliptical and a gas rich dwarf. The possibility of dating the globular clusters offers an efficient way of studying the history of violent star formation in this and similar galaxies.
2746. HST photometry of 74 galactic globular clusters
ID:
ivo://CDS.VizieR/J/A+A/391/945
Title:
HST photometry of 74 galactic globular clusters
Short Name:
J/A+A/391/945
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson B and V systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.
2747. HST photometry of 5 globular clusters
ID:
ivo://CDS.VizieR/J/AJ/147/4
Title:
HST photometry of 5 globular clusters
Short Name:
J/AJ/147/4
Date:
21 Oct 2021
Publisher:
CDS
Description:
We quantified and calibrated the metallicity and temperature sensitivities of colors derived from nine Wide-Field Camera 3 filters on board the Hubble Space Telescope using Dartmouth isochrones and Kurucz atmosphere models. The theoretical isochrone colors were tested and calibrated against observations of five well studied galactic clusters, M92, NGC 6752, NGC 104, NGC 5927, and NGC 6791, all of which have spectroscopically determined metallicities spanning -2.30<[Fe/H]<+0.4. We found empirical corrections to the Dartmouth isochrone grid for each of the following color-magnitude diagrams (CMDs): (F555W-F814W, F814W), (F336W-F555W, F814W), (F390M-F555W, F814W), and (F390W-F555W, F814W). Using empirical corrections, we tested the accuracy and spread of the photometric metallicities assigned from CMDs and color-color diagrams (which are necessary to break the age-metallicity degeneracy). Testing three color-color diagrams [(F336W-F555W),(F390M-F555W),(F390W-F555W), versus (F555W-F814W)], we found the colors (F390M-F555W) and (F390W-F555W) to be the best suited to measure photometric metallicities. The color (F390W-F555W) requires much less integration time, but generally produces wider metallicity distributions and, at very low metallicity, the metallicity distribution function (MDF) from (F390W-F555W) is ~60% wider than that from (F390M-F555W). Using the calibrated isochrones, we recovered the overall cluster metallicity to within ~0.1dex in [Fe/H] when using CMDs (i.e., when the distance, reddening, and ages are approximately known). The measured MDF from color-color diagrams shows that this method measures metallicities of stellar clusters of unknown age and metallicity with an accuracy of ~0.2-0.5dex using F336W-F555W, ~0.15-0.25dex using F390M-F555W, and ~0.2-0.4dex with F390W-F555W, with the larger uncertainty pertaining to the lowest metallicity range.
2748. HST photometry of globulars in M81 (NGC 3031)
ID:
ivo://CDS.VizieR/J/AJ/142/183
Title:
HST photometry of globulars in M81 (NGC 3031)
Short Name:
J/AJ/142/183
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform aperture photometry and profile fitting on 419 globular cluster (GC) candidates with m_V_<=23mag identified in Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) BVI imaging, and estimate the effective radii of the clusters. We identify 85 previously known spectroscopically confirmed clusters, and newly identify 136 objects as good cluster candidates within the 3{sigma} color and size ranges defined by the spectroscopically confirmed clusters, yielding a total of 221 probable GCs. The luminosity function peak for the 221 probable GCs with estimated total dereddening applied is V~(20.26+/-0.13)mag, corresponding to a distance of ~3.7+/-0.3Mpc. The blue and red GC candidates, and the metal-rich and metal-poor spectroscopically confirmed clusters, respectively, are similar in half-light radius. Red confirmed clusters are about 6% larger in median half-light radius than blue confirmed clusters, and red and blue good GC candidates are nearly identical in half-light radius. The total population of confirmed and "good" candidates shows an increase in half-light radius as a function of galactocentric distance.
2749. HST photometry of IC 883 star clusters
ID:
ivo://CDS.VizieR/J/AJ/143/16
Title:
HST photometry of IC 883 star clusters
Short Name:
J/AJ/143/16
Date:
21 Oct 2021
Publisher:
CDS
Description:
New optical Hubble Space Telescope (HST), Spitzer Space Telescope, Galaxy Evolution Explorer, and Chandra observations of the single-nucleus, Luminous InfraRed Galaxy (LIRG) merger IC 883 are presented. The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS) and is of particular interest for a detailed examination of a luminous late-stage merger due to the richness of the optically visible star clusters and the extended nature of the nuclear X-ray, mid-IR, CO, and radio emission. In the HST Advanced Camera for Surveys images, the galaxy is shown to contain 156 optically visible star clusters distributed throughout the nuclear regions and tidal tails of the merger, with a majority of visible clusters residing in an arc ~3-7kpc from the position of the mid-infrared core of the galaxy. The luminosity functions of the clusters have an {alpha}_F435W_~-2.17 +/-0.22 and {alpha}_F814W_~-2.01+/-0.21, compared with V-band-derived values measured for the well-studied LIRG NGC 34 and the Antennae Galaxy of {alpha}~-1.7+/-0.1 and -2.13+/-0.07, respectively.
2750. HST photometry of I Zw 18 massive stars
ID:
ivo://CDS.VizieR/J/ApJ/452/238
Title:
HST photometry of I Zw 18 massive stars
Short Name:
J/ApJ/452/238
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blue compact dwarf galaxies are tiny galaxies that are dominated by intense star-forming regions. Thus, they have been thought to represent a different and extreme environment for star formation compared to the Milky Way and many other nearby galaxies. In this paper we use images obtained with the Hubble Space Telescope to resolve the main body of one of these galaxies, I Zw 18, into stars for the first time. This galaxy is also one of the most metal-poor galaxies known and is sometimes argued to be evolutionarily young. Broadband colors are used to determine the bulk characteristics of the resolved stellar population to an F555W magnitude of about 26, or M_(V,0)~-4 (O9.5 V star). Narrow-band images are used to look for emission characteristic of Wolf-Rayet stars. Color-magnitude diagrams reveal a broad main sequence of massive stars as well as blue and red supergiants, although there is a surprising lack of Wolf-Rayet stars. About half the massive stars are located in two groups, corresponding to the two knots of emission identified in ground-based images, and the rest are distributed between these regions and in the outer parts of the galaxy. We find that the northwestern of these two regions resolves in Halpha images into a small H II region plus a complicated shell structure that encircles the northern stellar association. There are additional, larger loops and filaments of ionized gas up to 450pc from the center of the galaxy. While the shell could be as young as the stars it encircles, the larger ionized gas structures must be older for reasonable models, and their presence implies that there has been a previous generation of massive stars at least several tens of millions of years ago. However, we find no evidence in these data for stars that must be older than this. The larger sites of most recent star formation are located northwest and south of the central part of the galaxy. Thus, we find that I Zw 18 is somewhat more complicated than had previously been thought, both in terms of its star formation history and the state of its interstellar medium. At the same time, however, the stellar populations look relatively normal, and the spatial concentration of massive stars is closer to that of large OB associations in nearby galaxies rather than to that exemplified by the compact cluster R136 in the Large Magellanic Cloud.