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- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/397/899
- Title:
- Proper motions of field HB stars
- Short Name:
- J/A+A/397/899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We set new limits on the mass of the Milky Way, making use of the latest kinematic information for Galactic satellites and halo objects. Our sample consists of 11 satellite galaxies, 137 globular clusters, and 413 field horizontal-branch (FHB) stars up to distances of 10kpc from the Sun. Roughly half of the objects in this sample have measured proper motions, permitting the use of their full space motions in our analysis. The field horizontal branch stars presented in table1 was created from the list of Wilhelm 1999 (J/AJ/117/2329) as the source of magnitudes, radial velocities and [Fe/H]; the proper motions were extracted from one or more proper-motion catalogs: STARNET Catalog (Roeser 1996), Yale-San Juan Southern Proper Motion Catalog (SPM 2.0: Platais et al. 1998, Cat. I/283), Lick Northern Proper Motion Catalog (NPM1: Klemola et al. 1994, Cat. I/199), and TYCHO-2 Catalog (Hog et al. 2000, Cat. I/259).
- ID:
- ivo://CDS.VizieR/J/A+A/528/A127
- Title:
- Radial velocities in the globular NGC 2808
- Short Name:
- J/A+A/528/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation mechanism of hot horizontal branch (HB) stars is still one of the most uncertain points of stellar evolution theories. In the past decade, models based on their binary origin have been very successful in reproducing the properties of field subdwarf-B stars, but the observations of their analogues in globular clusters has posed new problems. In addition, the discovery of multiple populations offered an appealing alternative scenario for the formation of these stars. We search for binaries of period P<=200days among a sample of 83 blue horizontal branch stars (Teff=12000-22000K) in NGC 2808, a cluster known to host three distinct stellar populations and a multimodal horizontal branch. The final sample, after the rejection of stars with incomplete observations or poor quality data, consists of 64 targets. The radial velocity of the targets was measured in fourteen epochs, spanning a temporal interval of ~75days. The significant variations were identified by means of a detailed error analysis and a statistical study.
- ID:
- ivo://CDS.VizieR/J/ApJ/721/L28
- Title:
- Red clump stars in Galactic Bulge from OGLE-III
- Short Name:
- J/ApJ/721/L28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The red clump (RC) is found to be split into two components along several sightlines toward the Galactic bulge. This split is detected with high significance toward the areas (-3.5<l<1,b<-5) and (l,b)=(0,+5.2), i.e., along the bulge minor axis and at least 5 deg off the plane. The fainter (hereafter "main") component is the one that more closely follows the distance-longitude relation of the bulge RC. The main component is ~0.5mag fainter than the secondary component and with an overall approximately equal population. For sightlines further from the plane, the difference in brightness increases, and more stars are found in the secondary component than in the main component. The two components have very nearly equal (V-I) color.
- ID:
- ivo://CDS.VizieR/J/PAZh/34/868
- Title:
- Red giant clump in the Tycho-2 catalog
- Short Name:
- J/PAZh/34/868
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Tycho-2 proper motions and Tycho-2 and 2MASS photometry are used to select 97348 red giant clump (RGC) stars. The interstellar extinction and photometric distance are calculated for each of the stars. The selected stars are shown to form a selection-unbiased sample of RGC stars within about 350 pc of the Sun with the addition of more distant stars. The distribution of the selected stars in space and their motion are consistent with the assumption that the RGC contains Galactic disk stars with various ages and metallicities, including a significant fraction of stars younger than 1Gyr with masses of more than 2 solar masses. These young stars show differences of their statistical characteristics from those of older RGC stars, including differences in the variations of their distribution density with distance from the Galactic plane and in the dispersion of their velocities found using radial velocities and proper motions. The Sun has been found to rise above the Galactic plane by 13+/-1pc. The distribution density of the stars under consideration in space is probably determined by the Local Spiral Arm and the distribution of absorbing matter in the plane of the Gould Belt. Data are also available at: http://www.geocities.com/orionspiral/
- ID:
- ivo://CDS.VizieR/J/AJ/155/71
- Title:
- RGB & HB members of the bulge cluster NGC 6569
- Short Name:
- J/AJ/155/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometric and spectroscopic analyses have shown that the Galactic bulge cluster Terzan 5 hosts several populations with different metallicities and ages that manifest as a double red horizontal branch (HB). A recent investigation of the massive bulge cluster NGC 6569 revealed a similar, though less extended, HB luminosity split, but little is known about the cluster's detailed chemical composition. Therefore, we have used high-resolution spectra from the Magellan-M2FS and VLT-FLAMES spectrographs to investigate the chemical compositions and radial velocity distributions of red giant branch and HB stars in NGC 6569. We found the cluster to have a mean heliocentric radial velocity of -48.8 km/s ({sigma}=5.3 km/s; 148 stars) and <[Fe/H]>=-0.87 dex (19 stars), but the cluster's 0.05 dex [Fe/H] dispersion precludes a significant metallicity spread. NGC 6569 exhibits light- and heavy-element distributions that are common among old bulge/inner Galaxy globular clusters, including clear (anti)correlations between [O/Fe], [Na/Fe], and [Al/Fe]. The light-element data suggest that NGC 6569 may be composed of at least two distinct populations, and the cluster's low <[La/Eu]>=-0.11 dex indicates significant pollution with r-process material. We confirm that both HBs contain cluster members, but metallicity and light-element variations are largely ruled out as sources for the luminosity difference. However, He mass fraction differences as small as {Delta}Y~0.02 cannot be ruled out and may be sufficient to reproduce the double HB.
- ID:
- ivo://CDS.VizieR/J/other/IBVS/6106
- Title:
- RR Lyrae stars in GCVS observed by the QES
- Short Name:
- J/other/IBVS/610
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the light curve archive of the Qatar Exoplanet Survey to investigate the RR Lyrae variable stars listed in the GCVS. Of 588 variables studied, we reclassified 14 as eclipsing binaries, one as an RS CVn type variable, one as an irregular variable, four as classical Cepheids, and one as a type II Cepheid, while also improving their periods. We also report new RR Lyrae sub-type classifications for 65 variables and improve on the GCVS period estimates for 135 RR Lyrae variables. There are seven double-mode RR Lyrae stars in the sample for which we measured their fundamental and first overtone periods. Finally, we detected the Blazhko effect in 38 of the RR Lyrae stars for the first time and we successfully measured the Blazhko period for 26 of them.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/79
- Title:
- SDSS-DR8 BHB stars in the Milky Way's halo
- Short Name:
- J/ApJ/738/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative "close pair distribution" as a statistic in the four-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20kpc from the Galactic center exhibit stronger substructure than at r_gc_<20kpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/130
- Title:
- SDSS-DR7 red HB stars spectroscopic data
- Short Name:
- J/ApJ/751/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have selected 556 red horizontal branch stars along the streams of the Sagittarius (Sgr) dwarf galaxy from Sloan Digital Sky Survey DR7 spectroscopic data using a theoretical model. The metallicity and {alpha}-element distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [{alpha}/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distribution between the leading and trailing arms of the Sgr tidal tails. The metallicity and [{alpha}/Fe] distribution of the leading arm is similar to that of the Galaxy. The trailing arm is composed mainly of a metal-rich component and [{alpha}/Fe] is obviously lower than that of the Galactic stars. The metallicity gradient is -(1.8+/-0.3)x10^-3^dex/deg in the first wrap of the trailing arm and -(1.5+/-0.4)x10^-3^dex/deg in the first wrap of the leading arm. No significant gradient exists along the second wraps of the leading or trailing arms. It seems that the Sgr dwarf galaxy initially lost the metal-poor component in the second wrap (older) arms due to the tidal force of our Galaxy and then the metal-rich component is disrupted in the first wrap (younger) arms. Finally, we found that the velocity dispersion of the trailing arm from 88{deg}<{Lambda}_{sun}_<112{deg} is {sigma}=9.808+/-1.0km/s, which is consistent with previous work in the literature.
