- ID:
- ivo://CDS.VizieR/J/A+A/651/A102
- Title:
- Photometry of M31 globular cluster EXT8
- Short Name:
- J/A+A/651/A102
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We recently found the globular cluster (GC) EXT8 in M31 to have an extremely low metallicity of [Fe/H]=-2.91+/-0.04 using high-resolution spectroscopy. Here we present a colour-magnitude diagram (CMD) for EXT8, obtained with the Wide Field Camera 3 on board the Hubble Space Telescope. Compared with the CMDs of metal-poor Galactic GCs, we find that the upper red giant branch (RGB) of EXT8 is about 0.03mag bluer in F606W-F814W and slightly steeper, as expected from the low spectroscopic metallicity. The observed colour spread on the upper RGB is consistent with being caused entirely by the measurement uncertainties, and we place an upper limit of sigma(F606W-F814W)=0.015mag on any intrinsic colour spread. The corresponding metallicity spread can be up to sigma([Fe/H])=0.2dex or >0.7dex, depending on the isochrone library adopted. The horizontal branch (HB) is located mostly on the blue side of the instability strip and has a tail extending to at least M(F606W)=+3, as in the Galactic GC M15. We identify two candidate RR Lyrae variables and several UV-luminous post-HB/post-AGB star candidates, including one very bright (M(F300X)=-3.2) source near the centre of EXT8. The surface brightness of EXT8 out to a radius of 25 arcsec is well fitted by a Wilson-type profile with an ellipticity of epsilon=0.20, a semi-major axis core radius of 0.25", and a central surface brightness of 15.2mag per square arcsec in the F606W band, with no evidence of extra-tidal structure. Overall, EXT8 has properties consistent with it being a "normal", but very metal-poor GC, and its combination of relatively high mass and very low metallicity thus remains challenging to explain in the context of GC formation theories operating within the hierarchical galaxy assembly paradigm.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/529/A25
- Title:
- Photometry of star clusters in 5 nearby gal.
- Short Name:
- J/A+A/529/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. Ultimately this may lead to a better understanding of star formation in galaxies, and galaxy evolution in general. We aim to constrain the amount of star formation happening in long-lived clusters for four galaxies through the homogeneous, simultaneous study of field stars and star clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A144
- Title:
- Photometry of stars in the LeoA HST WFC3 field
- Short Name:
- J/A+A/614/A144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- LeoA is an isolated gas-rich dwarf irregular galaxy of low stellar mass and metallicity residing at the outskirts of the Local Group. Ages of the stellar populations in LeoA range from ~10Myr to ~10Gyr. A large stellar halo (up to the deprojected distance of ~1.7kpc was discovered based on Subaru wide-field photometry of red giant branch stars. We analysed HST WFC3 archive observation data in the field that is partly located beyond the previously known limits of the LeoA galaxy. We performed photometry of star-like objects in the F475W and F814W passbands and studied the spatial distribution of the Leo A stars below the horizontal branch. We report a discovery of stellar halo populations (subgiants and faint red giants) in the Leo A galaxy extending up to ~2.3kpc deprojected distance from the galaxy centre. Analysis of the colour-magnitude diagram suggests old (>5Gyr) stellar populations of very low metallicity (Z~0.0001).
- ID:
- ivo://CDS.VizieR/J/AJ/161/138
- Title:
- Photometry of 38708 stars in W3 complex with HST
- Short Name:
- J/AJ/161/138
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- We have used archival infrared images obtained with the Wide Field Camera 3 on board the Hubble Space Telescope to constrain the initial mass function of low-mass stars and brown dwarfs in the W3 star-forming region. The images cover 438arcmin^2^, which encompasses the entire complex, and were taken in the filters F110W, F139M, and F160W. We have estimated extinctions for individual sources in these data from their colors and have dereddened their photometry accordingly. By comparing an area of the images that contains the richest concentration of previously identified W3 members to an area that has few members and is dominated by background stars, we have estimated the luminosity function for members of W3 with masses of 0.03-0.4M{sun}. That luminosity function closely resembles data in typical nearby star-forming regions that have much smaller stellar populations than W3 ( ~500 versus several thousand objects). Thus, we do not find evidence of significant variations in the initial mass function of low-mass stars and brown dwarfs with star-forming conditions, which is consistent with recent studies of other distant massive star-forming regions.
- ID:
- ivo://CDS.VizieR/J/A+A/549/A47
- Title:
- Position and photometry of stars in SDIG
- Short Name:
- J/A+A/549/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the resolved stellar populations and derive the star formation history of the Sculptor dwarf irregular galaxy (SDIG), a gas-rich dwarf galaxy member of the NGC 7793 subgroup in the Sculptor group of galaxies. We constructed a colour - magnitude diagram (CMD) using archival observations from the Hubble Space Telescope/Advanced Camera for Surveys in order to examine the stellar content of SDIG, as well as the spatial distribution of stars selected within different stellar evolutionary phases. We derived the star formation history of SDIG using a maximum-likelihood fit to the CMD.
- ID:
- ivo://CDS.VizieR/J/ApJ/710/1032
- Title:
- Proper motions in {omega} Cen
- Short Name:
- J/ApJ/710/1032
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze data from the Hubble Space Telescope's (HST) Advanced Camera for Surveys of the globular cluster (GC) Omega Cen. We construct a photometric catalog of 1.2x10^6^ stars over a 10'x10' central field down to below B_F435W_=25 (M~0.35M_{sun}_). The 2.5 to 4 year baseline between observations yields a catalog of some 10^5^ proper motions over a smaller area, with 53382 "high-quality" measurements in a central R<~2' field. Artificial-star tests characterize the photometric incompleteness. We determine the cluster center to ~1" accuracy from star counts using two different methods, one based on isodensity contours and the other on "pie slices." We independently confirm the result by determining also the kinematical center of the HST proper motions, as well as the center of unresolved light seen in Two Micron All Sky Survey data. All results agree to within their 1"-2" levels of uncertainty. The proper-motion dispersion of the cluster increases gradually inward, but there is no variation in kinematics with position within the central ~15": there is no dispersion cusp and no stars with unusually high velocities. We measure for the first time in any GC the variation in internal kinematics along the main sequence.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/100
- Title:
- Proper motions of Leo II member stars
- Short Name:
- J/ApJ/741/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use 14 year baseline images obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST) to derive a proper motion for one of the Milky Way's most distant dwarf spheroidal companions, Leo II, relative to an extragalactic background reference frame. Astrometric measurements are performed in the effective point-spread function formalism using our own developed code. An astrometric reference grid is defined using 3224 stars that are members of Leo II and brighter than a magnitude of 25 in the F814W band. We identify 17 compact extragalactic sources, for which we measure a systemic proper motion relative to this stellar reference grid. We derive a proper motion [{mu}_{alpha}_,{mu}_{delta}_]=[+104+/-113,-33+/-151]uas/yr for Leo II in the heliocentric reference frame. Though marginally detected, the proper motion yields constraints on the orbit of Leo II. Given a distance of d~230kpc and a heliocentric radial velocity v_r_=+79km/s, and after subtraction of the solar motion, our measurement indicates a total orbital motion v_G_=266.1+/-128.7km/s in the Galactocentric reference frame, with a radial component v_rG_=21.5+/-4.3km/s and tangential component v_tG_=265.2+/-129.4km/s. The small radial component indicates that Leo II either has a low-eccentricity orbit or is currently close to perigalacticon or apogalacticon distance. We see evidence for systematic errors in the astrometry of the extragalactic sources which, while close to being point sources, are slightly resolved in the HST images. We provide a detailed catalog of the stellar and extragalactic sources identified in the HST data which should provide a solid early-epoch reference for future astrometric measurements.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A29
- Title:
- Properties of galactic PNe central stars
- Short Name:
- J/A+A/593/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained multi-wavelength observations of compact Galactic planetary nebulae (PNe) to probe post-asymptotic giant branch (AGB) evolution from the onset of nebular ejection. We analyze new observations from Hubble Space Telescope to derive the masses and evolutionary status of their central stars (CSs) in order to better understand the relationship between the CS properties and those of the surrounding nebulae. We work with HST/WFC3 images of 51 targets obtained in a snapshot survey (GO-11657). The high spatial resolution of HST allows us to resolve these compact PNe and distinguish the CS emission from that of their surrounding PNe. The targets were imaged through the filters F200LP, F350LP, and F814W from which we derive Johnson V and I magnitudes. We derive CS bolometric luminosities and effective temperatures using the Zanstra technique, from a combination of HST photometry and ground-based spectroscopic data. We present new unique photometric measurements of 50 CSs, and derived effective temperatures and luminosities for most of them.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/85
- Title:
- Properties of giant arcs behind CLASH clusters
- Short Name:
- J/ApJ/817/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We developed an algorithm to find and characterize gravitationally lensed galaxies (arcs) to perform a comparison of the observed and simulated arc abundance. Observations are from the Cluster Lensing And Supernova survey with Hubble (CLASH). Simulated CLASH images are created using the MOKA package and also clusters selected from the high-resolution, hydrodynamical simulations, MUSIC, over the same mass and redshift range as the CLASH sample. The algorithm's arc elongation accuracy, completeness, and false positive rate are determined and used to compute an estimate of the true arc abundance. We derive a lensing efficiency of 4+/-1 arcs (with length >=6" and length-to-width ratio >=7) per cluster for the X-ray-selected CLASH sample, 4+/-1 arcs per cluster for the MOKA-simulated sample, and 3+/-1 arcs per cluster for the MUSIC-simulated sample. The observed and simulated arc statistics are in full agreement. We measure the photometric redshifts of all detected arcs and find a median redshift z_s_=1.9 with 33% of the detected arcs having z_s_>3. We find that the arc abundance does not depend strongly on the source redshift distribution but is sensitive to the mass distribution of the dark matter halos (e.g., the c-M relation). Our results show that consistency between the observed and simulated distributions of lensed arc sizes and axial ratios can be achieved by using cluster-lensing simulations that are carefully matched to the selection criteria used in the observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/798/23
- Title:
- Radial velocities of giant stars in NGC 6388
- Short Name:
- J/ApJ/798/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new radial velocity measurements for 82 stars, members of the Galactic globular cluster (GC) NGC 6388, obtained from ESO-VLT K-band Multi Object Spectrograph (KMOS) spectra acquired during the instrument Science Verification. The accuracy of the wavelength calibration is discussed and a number of tests of the KMOS response are presented. The cluster systemic velocity obtained (81.3+/-1.5km/s) is in very good agreement with previous determinations. While a hint of ordered rotation is found between 9" and 20" from the cluster center, where the distribution of radial velocities is clearly bimodal, more data are needed before drawing any firm conclusions. The acquired sample of radial velocities has also been used to determine the cluster velocity dispersion (VD) profile between ~9" and 70", supplementing previous measurements at r<2" and r>60" obtained with ESO-SINFONI and ESO-FLAMES spectroscopy, respectively. The new portion of the VD profile nicely matches the previous ones, better defining the knee of the distribution. The present work clearly shows the effectiveness of a deployable integral field unit in measuring the radial velocities of individual stars for determining the VD profile of Galactic GCs. It represents the pilot project for an ongoing large program with KMOS and FLAMES at the ESO-VLT, aimed at determining the next generation of VD and rotation profiles for a representative sample of GCs.
