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1541. Blue and yellow straggler stars in open clusters
ID:
ivo://CDS.VizieR/J/A+A/650/A67
Title:
Blue and yellow straggler stars in open clusters
Short Name:
J/A+A/650/A67
Date:
22 Feb 2022
Publisher:
CDS
Description:
Blue straggler stars are exotic objects present in all stellar environments whose nature and formation channels are still partially unclear. They seem to be particularly abundant in open clusters (OCs), thus offering a unique chance to tackle these problems statistically. We aim at building up a new and homogeneous catalogue of blue straggler stars (BSS) in Galactic OCs using Gaia to provide a more solid assessment of these stars membership. Then, we aim at exploring possible relationships of the straggler abundance with the parent cluster structural and dynamical parameters. As a by-product, we also search for possible yellow straggler stars (YSS), which are believed to be stragglers in a more advanced evolution stage. We employ photometry, proper motions, and parallaxes extracted from Gaia DR2 for 408 Galactic star clusters and searched for stragglers within them after performing a careful membership analysis. The number of BBS emerging from our more stringent, selection criteria turns out to be significantly smaller than in previous versions of this catalogue. OCs are therefore not anymore a preferable environment for this kind of stars. Besides, we found that BSS start to appear in clusters with ages larger than log(t)~8.7 and are therefore absent in very young star clusters. The present catalogue supersedes the previous one from Ahumada et al. (2007A&A...463..789A, Cat. J/A+A/463/789) in several ways: membership assessment, number of stragglers found, and so forth. The new list includes 889 BSS and 77 YSS candidates in 408 OCs. We expect this catalogue to be the basis for a new round of studies of blue and yellow straggler stars.
1542. Blue compact galaxies from SBS
ID:
ivo://CDS.VizieR/J/A+A/373/24
Title:
Blue compact galaxies from SBS
Short Name:
J/A+A/373/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
The work studies of the environment of low-mass galaxies with active star formation (SF) and a possible trigger of SF bursts due to gravitational interaction. Following the study by Taylor et al. (1995ApJS...99..427T), we extend the search for possible disturbing galaxies of various masses to a much larger sample of 86 BCGs from the sky region of the Second Byurakan survey (SBS). The BCG magnitudes and radial velocities are revised and up-dated. The sample under study is separated by the criteria: EW([O III]5007)>45{AA} and V_h_<6000km/s nd should be representative of all low-mass galaxies which experience SF bursts.
1543. Blue-core galaxies properties
ID:
ivo://CDS.VizieR/J/other/RAA/19.81
Title:
Blue-core galaxies properties
Short Name:
J/other/RAA/19.8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We select 107 blue-core galaxies from the MaNGA survey, studying their morphology, kinematics as well as the gas-phase metallicity. Our results are as follows: (i) In our sample, 26% of blue-core galaxies have decoupled gas-star kinematics, indicating external gas accretion; 15% have bar-like structure and 8% show post-merger features, such as tidal tails and irregular gas/star velocity field. All these processes/features, such as accreting external misaligned gas, interaction and bar, can trigger gas inflow. Thus the central star-forming activities lead to bluer colors in their centers (blue-core galaxies). (ii) By comparing with the SDSS DR7 star-forming galaxy sample, we find that the blue-core galaxies have higher central gas-phase metallicity than what is predicted by the local mass-metallicity relation. We explore the origin of the higher metallicity, finding that not only the blue-core galaxies, but also the flat-gradient and red-core galaxies all have higher metallicity. This can be explained by the combined effect of redshift and galaxy color.
1544. Blue diffuse dwarf galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/465/3977
Title:
Blue diffuse dwarf galaxies
Short Name:
J/MNRAS/465/3977
Date:
21 Oct 2021
Publisher:
CDS
Description:
The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ~150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43<12+log(O/H)<8.01), with ~20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ~1-33x10^-2^M_{sun}_/yr in HII regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M_*_/M_{sun}_)~=5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.
1545. Blue diffuse dwarf galaxies spectroscopic data
ID:
ivo://CDS.VizieR/J/MNRAS/448/2687
Title:
Blue diffuse dwarf galaxies spectroscopic data
Short Name:
J/MNRAS/448/2687
Date:
21 Oct 2021
Publisher:
CDS
Description:
Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ~100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45<12+log(O/H)<8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (<10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11<~M_B_<~-18) and low surface brightnesses (~23-25 mag/arcsec^2^), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078 M_{sun}_/yr. From our current subsample, BDD galaxies appear to be a population of non-quiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor star-forming galaxies, which traditional emission-line-based searches overlook.
1546. Blue early-type galaxies in Galaxy Zoo
ID:
ivo://CDS.VizieR/J/MNRAS/396/818
Title:
Blue early-type galaxies in Galaxy Zoo
Short Name:
J/MNRAS/396/818
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5<SFR<50M_{sun}_/yr). They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital Sky Survey Data Release 6 and their u-r colour. We select a volume-limited sample in the redshift range 0.02<z<0.05, corresponding to luminosities of approximately L* and above and with u-r colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties.
1547. Blue-H{alpha} objects in M33
ID:
ivo://CDS.VizieR/J/A+AS/140/309
Title:
Blue-H{alpha} objects in M33
Short Name:
J/A+AS/140/309
Date:
21 Oct 2021
Publisher:
CDS
Description:
For the purposes of a search for SS433 type objects, LBV stars and hypergiants in M33, we have carried out a photometry of blue stars in H{alpha} images of this galaxy. From 2332 listed OB stars, we have isolated 549 objects, which have H{alpha} excess over stars of the same V magnitude. Among them 81 emission stars (s) have been selected. About 60% of isolated objects found to be extended in H{alpha}, among them 154 diffuse (d) and 180 bubble-type (b) nebulae. 117 objects are compact (c) and faint H{alpha} sources. These groups are different in colour indices, H{alpha} fluxes, surface brightness and sizes. The most probable size of the H{alpha} nebulae is FWHM=10-14pc. There is evidence that their properties and location in the galaxy are defined by interstellar gas pressure and related to spiral arms. The d objects are HII regions with an embedded star. The b objects are probably envelopes around WR stars or SN remnants. Among s-type objects we isolated a group of 20 brightest stars, which in their average properties fit well to the parameters of blue hypergiants or LBV-type stars. The stars of intermediate brightness follow very well to blue Ia supergiants. The interstellar absorption derived from brightest H{alpha} stars is A_V_=0.93+/-0.05mag. We classify the faintest stars as blue Ib supergiants, their average absorption is A_V_~0.6mag. They are restricted in number by the limiting stellar magnitude in the original sample.
1548. Blue HB stars in SDSS
ID:
ivo://CDS.VizieR/J/AJ/127/899
Title:
Blue HB stars in SDSS
Short Name:
J/AJ/127/899
Date:
21 Oct 2021
Publisher:
CDS
Description:
We isolate samples of 733 bright (g<18) and 437 faint (g>18) high Galactic latitude blue horizontal-branch stars with photometry and spectroscopy in the Sloan Digital Sky Survey (SDSS). Comparison of independent photometric and spectroscopic selection criteria indicates that contamination from F and blue straggler stars is less than 10% for bright stars (g<18) and about 25% for faint stars (g>18), and this is qualitatively confirmed by proper motions based on the USNO-A (<I/252>) catalog as first epoch. Analysis of repeated observations shows that the errors in radial velocity are ~26km/s. A relation between absolute magnitude and color is established using the horizontal branches of halo globular clusters observed by SDSS. Bolometric corrections and colors are synthesized in the SDSS filters from model spectra. The redder stars agree well in absolute magnitude with accepted values for RR Lyrae stars. The resulting photometric distances are accurate to about 0.2mag, with a median of about 25kpc. Modest clumps in phase space exist and are consistent with the previously reported tidal stream of the Sagittarius dwarf galaxy.
1549. Blue horizontal branch stars
ID:
ivo://CDS.VizieR/J/AJ/108/1722
Title:
Blue horizontal branch stars
Short Name:
J/AJ/108/1722
Date:
21 Oct 2021
Publisher:
CDS
Description:
A complete sample of blue horizontal branch (BHB) stars in the magnitude range 13.0<V<16.5 is isolated in two Galactic fields that have previously been searched for RR Lyrae variables: SA 57 in the Northern Polar Cap and the Lick Astrograph field RR 7 in the Anticenter (l=183{deg}, b=+37{deg}). These BHB stars are a subset of the AF stars found in the Case Low-Dispersion Northern Survey; lists of these AF stars were made available by the late Nick Sanduleak. The completeness of the sample was confirmed by reference to the photometric survey of SA 57 by Stobie & Ishida (1987AJ93..... 624S) that is complete to fainter than V=18. In the color range 0.00<(B-V)_0_<+0.20, we can distinguish the BHB stars among these AF stars by comparing them both with well known local field horizontal branch (FHB) stars and also the BHB members of the halo globular clusters M3 and M92. The criteria for this comparison include (1) a (u-B)_K_ color index (derived from photoelectric observations using the Stromgren u filter and the Johnson B and V filters) that measures the size of the Balmer jump, (2) a spectrophotometric index A that measures the steepness of the Balmer jump, and (3) a parameter D_0.2_ that is the mean width of the H{gamma} and H{delta} Balmer lines measured at 20 percent of the continuum level. These criteria give consistent results in separating BHB stars from higher gravity main sequence AF stars in the color range 0.00<(B-V)_0_<+0.20. All three photometric and spectrophotometric criteria were measured for 35 stars in the SA 57 field and 37 stars in the RR 7 field that are in the color range (B-V)_0_<+0.23 and in the magnitude range 13.0<V<16.5. For a small number of additional stars only (u-B)_K_ was obtained. Among the AF stars that are fainter than B=13 and bluer than (B-V)_0_=+0.23, about half of those in the SA 57 field and about one third of those in the lower latitude RR 7 field are BHB stars. Isoabundance contours were located empirically in plots of the pseudoequivalent width versus (B-V)_0_ for the lines of Mg II A4481{AA}, Ca II A3933 {AA} and Fe I A4272{AA}. Solar abundances were defined by the data from main sequence stars in the Pleiades and Coma open clusters. Data from the BHB stars in M3 and M92 defined the [Fe/H]=1.5 and -2.2 isoabundance contours, respectively. Metallicities of all stars were estimated by interpolating the measured pseudoequivalent widths in these diagrams at the observed (B-V)_0_. The distribution of [Fe/H] found for the BHB stars in this way is very similar to that which we found for the RR Lyrae stars in the same fields using the Preston AS method. The space densities of these BHB stars were analyzed both separately and together with earlier observations of field BHB stars given by Arnold & Gilmore (1992MNRAS.257..225A), Sommer-Larsen & Christensen (1986MNRAS.219..537S), and Preston et al. (1991ApJ...375..121P). This analysis supports a two-component model for the halo of our Galaxy that is similar in many respects to that proposed by Hartwick [The Galaxy (Reidel, Dordrecht 1987)] although our discussion refers only to the region outside the solar circle. For Z>=35kpc, a classical spherical halo dominates which follows a R_gal_^-3.5^ space-density law and which has a HB morphology like that of the globular cluster M3 (i.e., approximately equal numbers of BHB and RR Lyrae stars). Closer to the galactic plane, there is an additional component with a much flatter galactic distribution (scale height ~2.2kpc near the Sun). The stars of the two components do not have significantly different metallicity distributions but do have slightly different distributions of the A parameter which measures the steepness of the Balmer jump; this is the only physical criterion (independent of spatial or kinematic considerations) which distinguishes between the two components. If present estimates of the local RR Lyrae star space density are correct, then the ratio of BHB stars to RR Lyrae stars is higher in the flatter halo component. The flat component would then have a bluer HB morphology (which could be interpreted as making it older) than the spherical component. In the solar neighborhood about 80 percent of the BHB stars come from the flat component and about 20 percent from the spherical component. More than half of the AF stars with V>13.0 and (B-V)_0_<+0.23 are not BHB stars but have surface gravities that are more like those expected for main sequence stars. Their measured metallicities lie in the range -0.2<[Fe/H]<-2.3. The more metal-poor of these stars are probably similar to the blue metal-poor stars that have been discussed by Preston et al. (1994AJ....108..538P) which, while they probably include globular cluster blue stragglers as a subset, must also comprise stars of other types.
1550. Blue horizontal branch stars catalog
ID:
ivo://CDS.VizieR/J/A+AS/109/171
Title:
Blue horizontal branch stars catalog
Short Name:
J/A+AS/109/171
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)

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