- ID:
- ivo://CDS.VizieR/J/AJ/113/1026
- Title:
- Fabry-Perot Observations of M15
- Short Name:
- J/AJ/113/1026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used an Imaging Fabry-Perot Spectrophotometer with the Sub-arcsecond Imaging Spectrograph on the Canada-France-Hawaii Telescope to measure velocities for 1534 stars in the globular cluster M15 (NGC 7078) with uncertainties between 0.5 and 10km/s. Combined with previous velocity samples, the total number of stars with measured velocities in M15 is 1597. An average seeing of 0.8" allowed us to obtain velocities for 144 stars within 10" of the center of M15, including 12 stars within 2". The velocity dispersion profile for M15 remains flat at a value of 11km/s from a radius of 0.4 into our innermost reliable point at 0.02 (0.06pc). Assuming an isotropic velocity dispersion tensor, this profile and the previously-published surface brightness profile can be equally well represented either by a stellar population whose M/L varies with radius from 1.7 in solar units at large radii to 3 in the central region, or by a population with a constant M/L of 1.7 and a central black hole of 1000M_{sun}_. A non-parametric mass model that assumes no black hole, no rotation, and isotropy constrains the mass density of M15 to better than 30% at a radius of 0.07 parsecs. The mass-density profile of this model is well represented by a power law with an exponent of -2.2, the value predicted by models of cluster core-collapse. Using the assumption of local thermodynamic equilibrium, we estimate the present-day mass function and infer a significant number of 0.6-0.7 M_{sun}_ objects in the central few parsecs, 85% of which may be in the form of stellar remnants. Not only do we detect rotation; we find that the position angle of the projected rotation axis in the central 10" is 100deg different from that of the whole sample. We also detect an increase in the amplitude of the rotation at small radii. Although this increase needs to be confirmed with better-seeing data, it may be the result of a central mass concentration. (Copyright) 1997 American Astronomical Society.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/651/1098
- Title:
- Faint X-ray sources in Terzan 5
- Short Name:
- J/ApJ/651/1098
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report our analysis of a Chandra X-ray observation of the rich globular cluster Terzan 5, in which we detect 50 sources to a limiting 1.0-6keV X-ray luminosity of 3x10^31^ergs/s within the half-mass radius of the cluster. Thirty-three of these have LX>10^32^ergs/s, the largest number yet seen in any globular cluster. In addition to the quiescent low-mass X-ray binary (LMXB; identified by Wijnands et al., 2005ApJ...618..883W), another 12 relatively soft sources may be quiescent LMXBs. We compare the X-ray colors of the harder sources in Terzan 5 to the Galactic center sources studied by Muno and collaborators (2003, Cat. <J/ApJ/589/225>) and find the Galactic center sources to have harder X-ray colors, indicating a possible difference in the populations. We cannot clearly identify a metallicity dependence in the production of low-luminosity X-ray binaries in Galactic globular clusters, but a metallicity dependence of the form suggested by Jordan et al. (2004, Cat. <J/ApJ/613/270>) for extragalactic LMXBs is consistent with our data.
- ID:
- ivo://CDS.VizieR/J/ApJ/710/332
- Title:
- Far-UV sources in M80
- Short Name:
- J/ApJ/710/332
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Advanced Camera for Surveys on Hubble Space Telescope, we have surveyed the far-ultraviolet (FUV) and near-ultraviolet (NUV) populations in the core region of M80. The color-magnitude diagram (CMD) reveals large numbers of blue and extreme horizontal branch stars and blue stragglers, as well as ~60 objects lying in the region of the CMD where accreting and detached white dwarf binaries are expected. Overall, the blue straggler stars are the most centrally concentrated population, with their radial distribution suggesting a typical blue straggler mass of about 1.2M_{sun}_. However, counterintuitively, the faint blue stragglers are significantly more centrally concentrated than the bright ones and a Kolmogorov-Smirnov test suggest only a 3.5% probability that both faint and bright blue stragglers are drawn from the same distribution. This may suggest that (some) blue stragglers get a kick during their formation. We have also been able to identify the majority of the known X-ray sources in the core with FUV bright stars. One of these FUV sources is a likely dwarf nova that was in eruption at the time of the FUV observations. This object is located at a position consistent with Nova 1860 AD, or T Scorpii. Based on its position, X-ray and UV characteristics, this system is almost certainly the source of the nova explosion. The radial distribution of the X-ray sources and of the cataclysmic variable candidates in our sample suggest masses >1M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/2099
- Title:
- Fast-rotating M-dwarf stars in NGC 2547
- Short Name:
- J/MNRAS/411/2099
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At fast rotation rates, the coronal activity of G- and K-type stars has been observed to "saturate" and then decline again at even faster rotation rates - a phenomenon dubbed "supersaturation". In this paper, we investigate coronal activity in fast-rotating M-dwarfs using deep XMM-Newton observations of 97 low-mass stars of known rotation period in the young open cluster NGC 2547 and combine these with published X-ray surveys of low-mass field and cluster stars of known rotation period.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A54
- Title:
- Fe, Mg, Ti in Galactic clusters
- Short Name:
- J/A+A/628/A54
- Date:
- 02 Nov 2021 11:16:10
- Publisher:
- CDS
- Description:
- We test the effects of non-local thermodynamic equilibrium (NLTE) on the spectra of FGK-type stars across a wide range of metallicity and to derive abundance of Fe, Mg, and Ti for a sample of Galactic star clusters. We extend the Payne fitting approach to draw on NLTE and LTE spectral models in order to determine stellar parameters and chemical abundances for the Gaia-ESO benchmark stars. We also analyse the medium-resolution Giraffe spectra of 742 stars in 13 open and globular clusters in the Milky Way galaxy. We show that this approach accurately recovers effective temperatures, surface gravities, and abundances of the benchmark stars and clusters members. The differences between NLTE and LTE stellar parameters are small for the metal-rich stars. However, for metal-poor stars [Fe/H]<-1, the NLTE estimates of Teff, log(g) and [Fe/H] are higher than LTE estimates, and the systematic offset increases with decreasing metallicity. Our LTE measurements of metallicities and abundances in the Galactic clusters are in a good agreement with the earlier literature studies. For the majority of these clusters, our study yields the first estimates of NLTE abundances of Fe, Mg and Ti. The NLTE [Fe/H] are systematically higher, whereas the average NLTE [Mg/Fe] abundance ratios are ~0.15dex lower, compared to LTE. All clusters investigated in this work appear homogeneous in Fe and Ti, with the intra-cluster abundance variations of less then 0.1dex. We confirm large dispersions of [Mg/Fe] ratios for NGC 2808, NGC 4833 and M 15. Our results shows that NLTE analysis change the mean abundance ratios in the clusters, but does not influence the intra-cluster abundance dispersions. Combining the Payne fitting approach with NLTE spectral models as input is a powerful tool for a detailed exploration of the large-scale spectroscopic stellar surveys.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A44
- Title:
- FLAMES observations of NGC6535
- Short Name:
- J/A+A/607/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand globular clusters (GCs) we need to comprehend how their formation process was able to produce their abundance distribution of light elements. In particular, we need to figure out which stars imprinted the peculiar chemical signature of GCs. One of the best way is to study the light-element anti-correlations in a large sample of GCs, analysed homogeneously. As part of our spectroscopic survey of GCs with FLAMES, we present here the results of our study of about 30 red giant member stars in the low-mass, low-metallicity Milky Way cluster NGC 6535. We measured its metallicity (finding [Fe/H]=-1.95, rms=0.04dex in our homogeneous scale) and other elements, in particular we concentrate here on O and Na abundances. These elements define the normal Na-O anti-correlation of classical GCs, making NGC 6535 perhaps the lowest mass cluster with confirmed presence of multiple populations. We updated the census of Galactic and extragalactic GCs for which a statement on the presence or absence of multiple populations can be made on the basis of high-resolution spectroscopy preferentially, or photometry and low-resolution spectroscopy otherwise, discussing the importance of mass and age of the clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/65
- Title:
- FLAMES observations of NGC 5128's globular clusters
- Short Name:
- J/ApJ/805/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the dynamical properties of 125 compact stellar systems (CSSs) in the nearby giant elliptical galaxy NGC 5128, using high-resolution spectra (R~26000) obtained with Very Large Telescope/FLAMES. Our results provide evidence for a new type of star cluster, based on the CSS dynamical mass scaling relations. All radial velocity (v_r_) and line-of-sight velocity dispersion ({sigma}_los_) measurements are performed with the penalized pixel fitting (ppxf) technique, which provided {sigma}_ppxf_ estimates for 115 targets. The {sigma}_ppxf_ estimates are corrected to the 2D projected half-light radii, {sigma}_1/2_, as well as the cluster cores, {sigma}_0_, accounting for observational/aperture effects and are combined with structural parameters, from high spatial resolution imaging, in order to derive total dynamical masses (M_dyn_) for 112 members of NGC5128's star cluster system. In total, 89 CSSs have dynamical masses measured for the first time along with the corresponding dynamical mass-to-light ratios ({sigma}_1/2_). We find two distinct sequences in the {gamma}^dyn^_V_-M_dyn_ plane, which are well approximated by power laws of the forms {gamma}^dyn^_V_{propto}M_dyn_^0.33+/-0.04^ and {gamma}^dyn^_V_{propto}M_dyn_^0.79+/-0.04^. The shallower sequence corresponds to the very bright tail of the globular cluster luminosity function (GCLF), while the steeper relation appears to be populated by a distinct group of objects that require significant dark gravitating components such as central massive black holes and/or exotically concentrated dark matter distributions. This result would suggest that the formation and evolution of these CSSs are markedly different from the "classical" globular clusters in NGC 5128 and the Local Group, despite the fact that these clusters have luminosities similar to the GCLF turnover magnitude. We include a thorough discussion of myriad factors potentially influencing our measurements.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A87
- Title:
- FLAMES observations of Terzan 8
- Short Name:
- J/A+A/561/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive globular clusters (GCs) contain at least two generations of stars with slightly different ages and clearly distinct light elements abundances. The Na-O anticorrelation is the best studied chemical signature of multiple stellar generations. Low-mass clusters appear instead to be usually chemically homogeneous. We are investigating low-mass GCs to understand what is the lower mass limit where multiple populations can form, mainly using the Na and O abundance distribution. We used VLT/FLAMES spectra of giants in the low-mass, metal-poor GC Terzan 8, belonging to the Sagittarius dwarf galaxy, to determine abundances of Fe, O, Na, alpha-, Fe-peak, and neutron-capture elements in six stars observed with UVES and 14 observed with GIRAFFE. The average metallicity is [Fe/H]=-2.27+/-0.03 (rms=0.08), based on the six high-resolution UVES spectra. Only one star, observed with GIRAFFE, shows an enhanced abundance of Na and we tentatively assign it to the second generation. In this cluster, at variance with what happens in more massive GCs, the second generation seems to represent at most a small minority fraction. We discuss the implications of our findings, comparing Terzan 8 with the other Sgr dSph GCs, to GCs and field stars in the Large Magellanic Cloud, Fornax, and in other dwarfs galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A26
- Title:
- Fornax 3D project. Globular clusters
- Short Name:
- J/A+A/637/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters (GCs) are found ubiquitously in massive galaxies and due to their old ages, they are regarded as fossil records of galaxy evolution. Spectroscopic studies of GC systems are often limited to the outskirts of galaxies, where GCs stand out against the galaxy background and serve as bright tracers of galaxy assembly. In this work we use the capabilities of the Multi Unit Explorer Spectrograph (MUSE) to extract a spectroscopic sample of 722 GCs in the inner regions (<3Reff) of 32 galaxies in the Fornax cluster. These galaxies were observed as part of the Fornax 3D project, a MUSE survey that targets early and late-type galaxies within the virial radius of Fornax. After accounting for the galaxy background in the GC spectra, we extracted line-of-sight velocities and determined metallicities of a subsample of 238 GCs. We found signatures of rotation within GC systems and comparing the GC kinematics and that of the stellar body shows that the angular momentum of the GC system reflects that of the stars, confirming the usefulness of GCs as kinematic tracers. While the red GCs prove to closely follow the metallicity profile of the host galaxy, the blue GCs show a large spread of metallicities but are generally more metal -poor than the host.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A86
- Title:
- Fornax dSph H4 globular cluster stars
- Short Name:
- J/A+A/585/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The globular cluster H4, located in the center of the Fornax dwarf spheroidal galaxy, is crucial for understanding the formation and chemical evolution of star clusters in low-mass galactic environments. H4 is peculiar because the cluster is significantly more metal-rich than the galaxy's other clusters, is located near the galaxy center, and may also be the youngest cluster in the galaxy. In this study, we present detailed chemical abundances derived from high-resolution (R~28000) spectroscopy of an isolated H4 member star for comparison with a sample of 22 nearby Fornax field stars. We find the H4 member to be depleted in the alpha-elements Si, Ca, and Ti with [Si/Fe]=-0.35+/-0.34, [Ca/Fe]=+0.05+/-0.08, and [Ti/Fe]=-0.27+/-0.23, resulting in an average [{alpha}/Fe]=-0.19+/-0.14. If this result is representative of the average cluster properties, H4 is the only known system with a low [{alpha}/Fe] ratio and a moderately low metallicity embedded in an intact birth environment. For the field stars we find a clear sequence, seen as an early depletion in [{alpha}/Fe] at low metallicities, in good agreement with previous measurements. H4 falls on top of the observed field star [{alpha}/Fe] sequence and clearly disagrees with the properties of Milky Way halo stars. We therefore conclude that within a galaxy, the chemical enrichment of globular clusters may be closely linked to the enrichment pattern of the field star population. The low [{alpha}/Fe] ratios of H4 and similar metallicity field stars in Fornax give evidence that slow chemical enrichment environments, such as dwarf galaxies, may be the original hosts of alpha-depleted clusters in the halos of the Milky Way and M31.
