- ID:
- ivo://CDS.VizieR/J/MNRAS/417/1823
- Title:
- Sombrero galaxy globular clusters
- Short Name:
- J/MNRAS/417/1823
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a large sample of over 200 integrated-light spectra of confirmed globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with the Deep Imaging Multi-Object Spectrograph (DEIMOS) instrument on the Keck telescope. A significant fraction of the spectra have signal-to-noise ratio levels high enough to allow measurements of GC metallicities using the method of Brodie & Huchra. We find a distribution of spectroscopic metallicities in the range -2.2<[Fe/H]<+0.1 that is bimodal, with peaks at [Fe/H]~-1.4 and -0.6. Thus, the GC system of the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a bimodal spectroscopic metallicity distribution supporting the long-held belief that colour bimodality reflects two metallicity subpopulations. This further suggests that the transformation from optical colour to metallicity for old stellar populations, such as GCs, is not strongly non-linear. We also explore the radial and magnitude distribution with metallicity for GC subpopulations but small number statistics prevent any clear trends in these distributions.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/382/1353
- Title:
- Spectral atlas of omega Cen post-MS stars
- Short Name:
- J/MNRAS/382/1353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectral atlas of the post-main-sequence population of the most massive Galactic globular cluster, omega Centauri. Spectra were obtained of more than 1500 stars selected as uniformly as possible from across the (B, B-V) colour-magnitude diagram of the proper motion cluster member candidates of van Leeuwen et al. (2000, Cat. <J/A+A/360/472>). The spectra were obtained with the 2dF multifibre spectrograph at the Anglo-Australian Telescope, and cover the approximate range {lambda}~3840-3940{AA} at a resolving power of {lambda}/{Delta}{lambda}~=2000. This constitutes the most comprehensible spectroscopic survey of a globular cluster. We measure the radial velocities, effective temperatures, metallicities and surface gravities by fitting ATLAS9 stellar atmosphere models. We analyse the cluster membership and stellar kinematics, interstellar absorption in the Ca II K line at 3933{AA}, the RR Lyrae instability strip and the extreme horizontal branch, the metallicity spread and bimodal CN abundance distribution of red giants, nitrogen and s-process enrichment, carbon stars, pulsation-induced Balmer line emission on the asymptotic giant branch (AGB), and the nature of the post-AGB and UV-bright stars. Membership is confirmed for the vast majority of stars, and the radial velocities clearly show the rotation of the cluster core. We identify long-period RR Lyrae-type variables with low gravity, and low-amplitude variables coinciding with warm RR Lyrae stars. A barium enhancement in the coolest red giants indicates that third dredge-up operates in AGB stars in omega Cen. This is distinguished from the pre-enrichment by more massive AGB stars, which is also seen in our data. The properties of the AGB, post-AGB and UV-bright stars suggest that red giant branch (RGB) mass loss may be less efficient at very low metallicity, [Fe/H]<<1, increasing the importance of mass loss on the AGB. The catalogue and spectra are made available via Centre Donnees de Strasbourg (CDS).
- ID:
- ivo://CDS.VizieR/J/A+A/392/1
- Title:
- Spectrophotometry of simulated Stellar Populations
- Short Name:
- J/A+A/392/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new set of evolutionary synthesis spectra are presented for Simple Stellar Populations (SSPs) covering ranges in metallicity from 0.02<=Z/Z_{sun}_<=2.5 and ages from 4*10^6^yr<=t<=16Gyr. They are based on the most recent isochrones from the Padova group that extend earlier models by the inclusion of the thermal pulsing AGB phase for stars in the mass range 2M_{sun}_<=m<=7M_{sun}_ in accordance with the fuel consumption theorem. We show that with respect to earlier models, inclusion of the TP-AGB phase leads to significant changes in the (V-I) and (V-K) colors of SSPs in the age range from 10^8^ to >~10^9^yr. Using model atmosphere spectra from Lejeune et al. (1997, Cat. <J/A+AS/125/229>, 1998, Cat. <J/A+AS/130/65>), we calculate the spectral evolution of single burst populations of various metallicities covering the wavelength range from 90{AA} through 160{mu}m. Isochrone spectra are convolved with filter response functions to describe the time evolution of luminosities and colors in Johnson, Thuan & Gunn, Koo, HST, Washington and Stroemgren filters. The models and their results are not only intended for use in the interpretation of star clusters but also for combination with any kind of dynamical galaxy formation and/or evolution model that contains a star formation criterion. Moreover, the evolution of these single burst single metallicity stellar populations is readily folded with any kind of star formation -- and eventually chemical enrichment -- history to describe the evolutionary spectral synthesis of composite stellar populations like galaxies of any type with continuous or discontinuous star formation. For these latter purposes we also present the time evolution of ejection rates for gas and metals for two different Initial Mass Functions (IMFs) as well as cosmological and evolutionary corrections for all the filters as a function of redshift for 0<=z<=5 and two different cosmologies.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/19
- Title:
- Spectroscopic HK' index for 3 globular clusters
- Short Name:
- J/ApJS/216/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is increasing evidence for the presence of multiple red giant branches (RGBs) in the color-magnitude diagrams of massive globular clusters (GCs). In order to investigate the origin of this split on the RGB, we have performed new narrow-band Ca photometry and low-resolution spectroscopy for M22, NGC 1851, and NGC 288. We find significant differences (more than 4{sigma}) in calcium abundance from the spectroscopic HK' index for M22 and NGC 1851. We also find more than 8{sigma} differences in CN-band strength between the Ca-strong and Ca-weak subpopulations for these GCs. For NGC 288, however, a large difference is detected only in the CN strength. The calcium abundances of RGB stars in this GC are identical to within the errors. This is consistent with the conclusion from our new Ca photometry where the RGB splits are confirmed in M22 and NGC 1851, but not in NGC 288. We also find interesting differences in the CN-CH correlations among these GCs. While CN and CH are anti-correlated in NGC 288, they show a positive correlation in M22. NGC 1851, however, shows no difference in CH between the two groups of stars with different CN strengths. We suggest that all of these systematic differences would be best explained by how strongly Type II supernovae enrichment has contributed to the chemical evolution of these GCs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/405/839
- Title:
- Spectroscopic observations of globular clusters
- Short Name:
- J/MNRAS/405/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of medium-resolution spectroscopy of 28 globular clusters (GCs) in six nearby galaxies of different luminosities and morphological types, situated in M33 (15 objects), M31 (three), IC10 (four), UGCA86 (four), Holmberg IX (one) and DDO71 (one) obtained at the Special Astrophysical Observatory 6-m telescope. Measurements of Lick absorption line indices and comparison with Simple Stellar Population models enabled us to obtain their spectroscopic ages, metallicities and {alpha}-element to Fe abundance ratios.
- ID:
- ivo://CDS.VizieR/J/ApJ/837/176
- Title:
- Spectroscopic obs. of 2 red giant stars in omega Cen
- Short Name:
- J/ApJ/837/176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a chemical abundance analysis of a metal-poor star, ROA276, in the stellar system {omega} Centauri. We confirm that this star has an unusually high [Sr/Ba] abundance ratio. Additionally, ROA 276 exhibits remarkably high abundance ratios, [X/Fe], for all elements from Cu to Mo along with normal abundance ratios for the elements from Ba to Pb. The chemical abundance pattern of ROA 276, relative to a primordial {omega} Cen star ROA 46, is best fit by a fast-rotating low-metallicity massive stellar model of 20M_{sun}_, [Fe/H]=-1.8, and an initial rotation 0.4 times the critical value; no other nucleosynthetic source can match the neutron-capture element distribution. ROA 276 arguably offers the most definitive proof to date that fast-rotating massive stars contributed to the production of heavy elements in the early universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/104
- Title:
- Spectroscopic obs. of RR Lyrae in NGC5139
- Short Name:
- J/ApJ/881/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC5139 ({omega} Cen). We collected optical (4580-5330{AA}), high-resolution (R~34000), high signal-to-noise ratio (~200) spectra for 113 RRLs with the multifiber spectrograph M2FS at the Magellan/Clay Telescope at Las Campanas Observatory. We also analyzed high- resolution (R~26000) spectra for 122 RRLs collected with FLAMES/GIRAFFE at the Very Large Telescope, available in the ESO archive. The current sample doubles the literature abundances of cluster and field RRLs in the Milky Way based on high-resolution spectra. Equivalent-width measurements were used to estimate atmospheric parameters, iron, and abundance ratios for {alpha} (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn), and s-process (Y) elements. We confirm that {omega}Cen is a complex cluster, characterized by a large spread in the iron content: -2.58<~[Fe/H]<~-0.85. We estimated the average cluster abundance as <[Fe/H]>=-1.80{+/-}0.03, with {sigma}=0.33dex. Our findings also suggest that two different RRL populations coexist in the cluster. The former is more metal-poor ([Fe/H]<~-1.5), with almost solar abundance of Y. The latter is less numerous, more metal-rich, and yttrium enhanced ([Y/Fe]>~0.4). This peculiar bimodal enrichment only shows up in the s-process element, and it is not observed among lighter elements, whose [X/Fe] ratios are typical for Galactic globular clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1117
- Title:
- Spectroscopic study of red giants in M15
- Short Name:
- J/AJ/135/1117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectra of 110 selected red giant stars in the globular cluster M15 (NGC 7078) were obtained with Hectochelle at the MMT telescope in 2005 May, 2006 May, and 2006 October. Echelle orders containing H{alpha} and CaII H&K are used to identify emission and line asymmetries characterizing motions in the extended atmospheres. Emission in H{alpha} is detected to a luminosity of log(L/L_{sun}_)=2.36, in this very metal-deficient cluster, comparable to other studies, suggesting that the appearance of emission wings is independent of stellar metallicity. The faintest stars showing H{alpha} emission appear to lie on the asymptotic giant branch (AGB) in M15. A line-bisector technique for H{alpha} reveals outflowing velocities in all stars brighter than log(L/L_{sun}_)=2.5, and this outflow velocity increases with stellar luminosity, indicating the mass outflow increases smoothly with luminosity. Many stars lying low on the AGB show exceptionally high outflow velocities (up to 10-15km/s) and more velocity variability (up to 6-8km/s) than red giant branch (RGB) stars of similar apparent magnitude. High velocities in M15 may be related to the low cluster metallicity. Dusty stars identified from Spitzer Space Telescope infrared photometry as AGB stars are confirmed as cluster members by radial velocity measurements, yet their H{alpha} profiles are similar to those of RGB stars without dust. If substantial mass loss creates the circumstellar shell responsible for infrared emission, such mass loss must be episodic.
- ID:
- ivo://CDS.VizieR/J/AJ/112/1489
- Title:
- Spectroscopic survey for binaries in NGC 5053
- Short Name:
- J/AJ/112/1489
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried our a radial velocity survey for spectroscopic binaries in the low-density globular cluster NGC 5053. Our sample contains a total of 77 cluster member giant and subgiant stars with visual magnitudes of 14.5-18.6. Of These 77 stars, 66 stars have on average of 3-4 measurements with a total of 236 velocities. A typical velocity error per measurement is 13km/s. The stars in our sample are spatially distributed from the cluster center out to 10arcmin in radius (4.5 core radii). Among theses 66 stars with multiple velocity measurements, we discovered 6 spectroscopic binary candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A27
- Title:
- Spectroscopy in Galactic globular clusters
- Short Name:
- J/A+A/540/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Well determined radial velocities and abundances are essential for analyzing the properties of the Globular Cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the CaII triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present signifiant revisions of the existing velocities or abundances, or both.
