- ID:
- ivo://CDS.VizieR/J/ApJ/797/43
- Title:
- Blue stragglers in {omega} Cen
- Short Name:
- J/ApJ/797/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By using high-resolution spectra acquired with FLAMES-GIRAFFE at the ESO/VLT, we measured the radial and rotational velocities for 110 blue straggler stars (BSSs) in {omega} Centauri, the globular cluster-like stellar system harboring the largest known BSS population. According to their radial velocities, 109 BSSs are members of the system. The rotational velocity distribution is very broad, with the bulk of BSSs spinning at less than ~40 km/s (in agreement with the majority of such stars observed in other globular clusters) and a long tail reaching ~200km/s. About 40% of the sample has v_e_sini>40km/s and about 20% has v_e_sini>70km/s. Such a large fraction is very similar to the percentage of fast rotating BSSs observed in M4. Thus, {omega} Centauri is the second stellar cluster, beyond M4, with a surprisingly high population of fast spinning BSSs. We found a hint of radial behavior for a fraction of fast rotating BSSs, with a mild peak within one core radius, and a possible rise in the external regions (beyond four core radii). This may suggest that recent formation episodes of mass transfer BSSs occurred preferentially in the outskirts of {omega} Centauri, or that braking mechanisms able to slow down these stars are least efficient in the lowest density environments.
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- ID:
- ivo://CDS.VizieR/J/ApJ/797/82
- Title:
- Brightest cluster galaxies in Abell clusters
- Short Name:
- J/ApJ/797/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained photometry and spectroscopy of 433 z<=0.08 brightest cluster galaxies (BCGs) in a full-sky survey of Abell clusters to construct a BCG sample suitable for probing deviations from the local Hubble flow. This sample allows us to explore the structural and photometric properties of BCGs at the present epoch, their location in their hosting galaxy clusters, and the effects of the cluster environment on their structure and evolution. We revisit the L_m_-{alpha} relation for BCGs, which uses {alpha}, the log-slope of the BCG photometric curve of growth, to predict the metric luminosity in an aperture with 14.3kpc radius, L_m_, for use as a distance indicator. We measure central stellar velocity dispersions, {sigma}, of the BCGs.
- ID:
- ivo://CDS.VizieR/J/ApJ/440/28
- Title:
- Brightest Cluster Galaxies velocities
- Short Name:
- J/ApJ/440/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the use of Brightest Cluster Galaxies (BCGs) as standard candles for measuring galaxy peculiar velocities on large scales. We have obtained precise large-format CCD surface photometry and redshifts for an all-sky, volume-limited (z<=0.05) sample of 119 BCG. We reinvestigate the Hoessel (1980ApJ...241..493H) relationship between the metric luminosity, L_m_, within the central 10h^-1^kpc of the BCGs and the logarithmic slope of the surface brightness profile, {alpha}. The L_m_-{alpha} relationship reduces the cosmic scatter in L_m_ from 0.327mag to 0.244mag, yielding a typical distance accuracy of 17% per BCG. Residuals about the L_m_-{alpha} relationship are independent of BCG luminosity, BCG B-R_c_ color, BCG location within the host cluster, and richness of the host cluster. The metric luminosity is independent of cluster richness even before correcting for its dependence on {alpha}, which provides further evidence for the unique nature of the BCG luminosity function. Indeed, the BCG luminosity function, both before and after application of the {alpha}-correction, is consistent with a single Gaussian distribution. Half the BCGs in the sample show some evidence of small color gradients as a function of radius within their central 50h^-1^kpc regions but with almost equal numbers becoming redder as becoming bluer. However, with the central 10h^-1^kpc the colors are remarkably constant, the mean B-R_c_ color is 1.51 with a dispersion of only 0.06mag. The narrow photometric and color distributions of the BCGs, the lack of "second-parameter" effects, as well as the unique rich cluster environment of BCGs, argue that BCGs are the most homogeneous distance indicators presently available for large-scale structure research.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/405
- Title:
- Brightest galaxies in Local Volume
- Short Name:
- J/MNRAS/440/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Distances and near-infrared luminosities of the brightest galaxies in the Local Volume have been re-evaluated in order to gain a fully homogeneous collection of data for elucidating the framework of the Local Sheet and its relevance to Local Group evolution. It is demonstrated that the Local Sheet is both geometrically and dynamically distinct from the Local Supercluster and that the evolution of the Sheet and Local Group were probably interconnected. The Sheet is inclined by 8{deg} with respect to the Local Supercluster, and the dispersion of giant members about the mid-plane is only 230kpc. A 'Council of Giants' with a radius of 3.75Mpc encompasses the Local Group, demarcating a clear upper limit to the realm of influence of the Local Group. The only two giant elliptical galaxies in the Sheet sit on opposite sides of the Council, raising the possibility that they have somehow shepherded the evolution of the Local Group. The position vector of the Andromeda galaxy with respect to the Milky Way deviates only 11{deg} from the Sheet plane and only 11{deg} from the projected axis of the ellipticals. The Local Group appears to be moving away from a ridge in the potential surface of the Council on a path parallel to the elliptical axis. Spin directions of the giants in the Council are distributed over the sky in a pattern which is very different from that of giants beyond, possibly in reaction to the central mass asymmetry that developed into the Local Group. By matching matter densities of Group and Council giants, the edge of the volume of space most likely to have contributed to the development of the Local Group is shown to be very close to where gravitational forces from the Local Group and the Council balance. The boundary specification reveals that the Local Sheet formed out of a density perturbation of very low amplitude (~10%), but that normal matter was incorporated into galaxies with relatively high efficiency (~40%). It appears that the development of the giants of the Local Sheet was guided by a pre-existing flattened framework of matter.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/2018
- Title:
- 6 bright Galactic Cepheids data
- Short Name:
- J/MNRAS/430/2018
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of photometric and spectroscopic data of six bright Galactic Cepheids: GH Carinae, V419 Centauri, V898 Centauri, AD Puppis, AY Sagittarii and ST Velorum. Based on new radial velocity data (in some cases supplemented with earlier data available in the literature), these Cepheids have been found to be members in spectroscopic binary systems. V898 Cen turned out to have one of the largest orbital radial velocity amplitude (>40km/s) among the known binary Cepheids. The data are insufficient to determine the orbital periods nor other orbital elements for these new spectroscopic binaries. These discoveries corroborate the statement on the high frequency of occurrence of binaries among the classical Cepheids, a fact to be taken into account when calibrating the period-luminosity relationship for Cepheids. We have also compiled all available photometric data that revealed that the pulsation period of AD Pup, the longest period Cepheid in this sample, is continuously increasing with {Delta}P=0.004567d/century, likely to be caused by stellar evolution. The wave-like pattern superimposed on the parabolic O-C graph of AD Pup may well be caused by the light-time effect in the binary system. ST Vel also pulsates with a continuously increasing period. The other four Cepheids are characterized with stable pulsation periods in the last half century.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/1585
- Title:
- Bright metal-poor stars from HES survey
- Short Name:
- J/ApJ/652/1585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 1777 bright (9<B<14) metal-poor candidates selected from the Hamburg/ESO Survey (HES). Despite saturation effects present in the red portion of the HES objective-prism spectra, the data were recoverable and quantitative selection criteria could be applied to select the sample. Analyses of medium-resolution (~2{AA}) follow-up spectroscopy of the entire sample, obtained with several 24m class telescopes, yielded 145 new metal-poor stars with metallicity [Fe/H]<-2.0, of which 79 have [Fe/H]<-2.5 and 17 have [Fe/H]<-3.0. We also obtained C/Fe estimates for all of these stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/81
- Title:
- Bright metal-poor stars from HES Survey. II.
- Short Name:
- J/ApJ/835/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9<B<14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel+ (2006, J/ApJ/652/1585; Paper I) analysis of these stars was able to derive estimates of [Fe/H] and [C/Fe] only for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of T_eff_, logg, [Fe/H], and [C/Fe] for almost the entire data set. This sample is very local-about 90% of the stars are located within 0.5kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman and MacConnell "weak metal" candidates by Beers+ (2014, J/ApJ/794/58). We use this combined sample to identify possible members of the halo stream of stars suggested by Helmi+ (1999Natur.402...53H) and Chiba & Beers (2000AJ....119.2843C), as well as stars that may be associated with stripped debris from the putative parent dwarf of the globular cluster Omega Centauri, suggested to exist by previous authors. We identify a clear increase in the cumulative frequency of carbon-enhanced metal-poor (CEMP) stars with declining metallicity, as well as an increase in the fraction of CEMP stars with distance from the Galactic plane, consistent with previous results. We also identify a relatively large number of CEMP stars with kinematics consistent with the metal-weak thick-disk population, with possible implications for its origin.
- ID:
- ivo://CDS.VizieR/J/A+A/466/157
- Title:
- Bulge Microlensing Events
- Short Name:
- J/A+A/466/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Microlensing events have been observed regularly by surveys such as MACHO, OGLE and MOA. They offer an excellent way to probe the galactic structure, kinematics and stellar content. We have undertaken a follow-up study of 16 galactic microlensing events to determine masses and locations of the sources of these events within the Galaxy. Spectroscopy allows us to obtain information about the sources of the events. Low resolution spectra obtained with the Magellan I and II telescopes were analyzed to obtain radial velocities, spectral type and extinction by the method of Kane & Sahu (2003ApJ...582..743K). We also present results for the lens of the event using the microlensing light curve when possible. Light curves have been analyzed with the standard and the parallax models. We have inferred a configuration inside our galaxy for each event, and therefore a lens mass estimation using a suitable galaxy model. Lens mass determination in some cases shows massive lenses that can be considered black hole candidates. This is the case for the events MACHO-98-BLG-6, and OGLE-00-BUL-43. In our sample only three events do not have enough parallax signal for a successful estimation of the lens mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/L25
- Title:
- Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR)
- Short Name:
- J/ApJ/821/L25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars (RRLs) exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RRLs predate these structures and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal-rich ([Fe/H]~-1dex) halo-bulge population.
- ID:
- ivo://CDS.VizieR/J/A+A/465/943
- Title:
- BVI and RV curves of 5 eclipsing binaries
- Short Name:
- J/A+A/465/943
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We detected tertiary components of close binaries from spectroscopy and light curve modelling, investigated the light-travel time effect and the possibility of magnetic activity cycles, measured mass ratios for unstudied systems, and derived absolute parameters. We carried out new photometric and spectroscopic observations of five bright close eclipsing binaries, predominantly in the southern skies. We obtained full Johnson BV light curves, which were modelled with the Wilson-Devinney code. Radial velocities were measured with the cross-correlation method using IAU radial velocity standards as spectral templates. Period changes were studied with the O-C method, utilising published epochs of minimum light (XY Leo) and ASAS photometry (VZ Lib). For three objects (DX Tuc, QY Hya, V870 Ara), absolute parameters have been determined for the first time. We spectroscopically detected the tertiary components in XY Leo and VZ Lib and discovered one in QY Hya. For XY Leo we updated the light-time effect parameters and detected a secondary periodicity of about 5100d in the O-C diagram that may hint at the existence of short-period magnetic cycles. A combination of recent photometric data shows that the orbital period of the tertiary star in VZ Lib is likely to be over 1500d. QY Hya is a semi-detached X-ray active binary in a triple system with K and M-type components, while V870 Ara is a contact binary with the third smallest spectroscopic mass ratio for a W UMa star to date. Being close to the theoretical minimum for contact binaries, this small mass ratio suggests that V870 Ara has the potential of constraining evolutionary scenarios of binary mergers. The inferred distances to these systems are compatible with the Hipparcos parallaxes.