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211. Blue and red spectra of {omega} Cen HB stars
ID:
ivo://CDS.VizieR/J/MNRAS/399/195
Title:
Blue and red spectra of {omega} Cen HB stars
Short Name:
J/MNRAS/399/195
Date:
21 Oct 2021
Publisher:
CDS
Description:
The multiphase interstellar medium (ISM) is highly structured, on scales from the size of the Solar System to that of a galaxy. In particular, small-scale structures are difficult to study and hence are poorly understood. We used the multiplex capabilities of the AAOmega spectrograph at the Anglo-Australian Telescope to create a half-square-degree map of the neutral and low-ionized ISM in front of the nearby (~5kpc), most massive Galactic globular cluster, {omega} Centauri. Its redshifted, metal-poor and hot horizontal branch stars probe the medium-strong CaII K and NaI D2 line absorption, and weak absorption in the {lambda}5780 and {lambda}5797 diffuse interstellar bands (DIBs), on scales around a parsec. The kinematical and thermodynamical picture emerging from these data is that we predominantly probe the warm neutral medium and weakly ionized medium of the Galactic Disc-Halo interface, ~0.3-1kpc above the mid-plane. A comparison with Spitzer Space Telescope 24um and DIRBE/IRAS maps of the warm and cold dust emission confirms that both NaI and CaII trace the overall column density of the warm neutral and weakly ionized medium. Clear signatures are seen of the depletion of calcium atoms from the gas phase into dust grains.
212. Blue and red supergiants in M33
ID:
ivo://CDS.VizieR/J/ApJS/89/85
Title:
Blue and red supergiants in M33
Short Name:
J/ApJS/89/85
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of blue and red stars in M33 based on photographic photometry of over 65,000 objects extracted from plates taken with the 3.6m Canada-France-Hawaii Telescope (CFHT) and the 2.0m Rozhen (Bulgarian) Telescope. The completeness limit of the various surveys are estimated here to be V=19.5mag for those stars situated in crowed associations, and V=20.0mag for stars in the interarm fields. We list magnitudes and positions for 2112 blue stars, defined by (U-V)<0.0mag, and V<19.5mag, and 389 red stars defined by (B-V)>1.8mag and V<19.5mag. Of these, 1156 are candidate O stars on the basis of (U-V)<-0.9mag.
213. 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.
214. 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.
215. 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.
216. 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.
217. Blue stars with disk photometry in NGC 6611
ID:
ivo://CDS.VizieR/J/A+A/521/A18
Title:
Blue stars with disk photometry in NGC 6611
Short Name:
J/A+A/521/A18
Date:
21 Oct 2021
Publisher:
CDS
Description:
NGC 6611 and its parental cloud, the Eagle Nebula (M 16), are well-studied star-forming regions, thanks to their large content of both OB stars and stars with disks and the observed ongoing star formation. In our previous studies of the Eagle Nebula, we identified 834 disk-bearing stars associated with the cloud, after detecting their excesses in NIR bands from J band to 8.0um. In this paper, we study in detail the nature of a subsample of disk-bearing stars that show peculiar characteristics. They appear older than the other members in the V vs. V-I diagram, and/or they have one or more IRAC colors at pure photospheric values, despite showing NIR excesses, when optical and infrared colors are compared.
218. Blue stragglers and variable stars in M3
ID:
ivo://CDS.VizieR/J/AJ/108/1786
Title:
Blue stragglers and variable stars in M3
Short Name:
J/AJ/108/1786
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper describes Hubble Space Telescope (HST)/Planetary Camera-I images of the core of the dense globular cluster M3 (NGC 5272). Stellar photometry in the F555W (V) and F785LP (I) bands, with a 1 sigma photometric accuracy of about 0.1mag, has been used to construct color-magnitude diagrams of about 4700 stars above the main-sequence turnoff within r<~1' of the cluster center. We have also analyzed archival HST F336W (U) images of M3 obtained by the Wide Field/Planetary Camera-I Instrument Definition Team. The UVI data are used to identify 28 blue straggler (BS) stars within the central 0.29arcmin^2. The specific frequency of BSs in this region of M3, N(BS)/N(V<V(HB)+2)=0.094+/-0.019, is about a factor of 2-3 higher than that found by Bolte et al. [1993, ApJ, 408, L89] in a recent ground-based study of the same region, but comparable to that seen in the sparse outer parts of the same cluster and in HST observations of the core of the higher density cluster 47 Tuc. The BSs in M3 are slightly more centrally concentrated than red giant branch stars while horizontal branch stars are somewhat less concentrated than red giants. The radial distribution of V-selected subgiant and turnoff stars is well fit by a King model with a core radius r(core)=28"+/-2" (90% confidence limits), which corresponds to 1.4pc. Red giant and horizontal branch stars selected in the ultraviolet data (U<18) have a somewhat more compact distribution (r(core)=22.5"). The HST U data consist of 17 exposures acquired over a span of three days. We have used these data to isolate 40 variable stars for which relative astrometry, brightnesses, colors, and light curves are presented. A Kolmogorov-Smirnov test indicates that, typically, the variability for each star is significant at the 95% level. We identify two variable BS candidates (probably of the SX Phe type) out of a sample of ~25 BSs in which variability could have been detected. Most of the variables are RR Lyrae stars on the horizontal branch. All of them have periods P>~8h.
219. Blue stragglers in NGC 6388
ID:
ivo://CDS.VizieR/J/ApJ/677/1069
Title:
Blue stragglers in NGC 6388
Short Name:
J/ApJ/677/1069
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used multiband high-resolution HST WFPC2 and ACS observations combined with wide-field ground-based observations to study the blue straggler star (BSS) population in the Galactic globular cluster NGC 6388. As in several other clusters we have studied, the BSS distribution is found to be bimodal: highly peaked in the cluster center, rapidly decreasing at intermediate radii, and rising again at larger radii. In other clusters the sparsely populated intermediate-radius region (or "zone of avoidance") corresponds well to that part of the cluster where dynamical friction would have caused the more massive BSSs or their binary progenitors to settle to the cluster center. Instead, in NGC 6388, BSSs still populate a region that should have been cleaned out by dynamical friction effects, thus suggesting that dynamical friction is somehow less efficient than expected. As a by-product of these observations, the peculiar morphology of the horizontal branch (HB) is also confirmed. In particular, within the (very extended) blue portion of the HB we are able to clearly characterize three subpopulations: ordinary blue HB stars, extreme HB stars, and blue hook stars. Each of these populations has a radial distribution which is indistinguishable from normal cluster stars.
220. Blue stragglers in open clusters
ID:
ivo://CDS.VizieR/J/A+A/463/789
Title:
Blue stragglers in open clusters
Short Name:
J/A+A/463/789
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalogue of blue-straggler candidates in galactic open clusters. It is based on the inspection of the colour-magnitude diagrams of the clusters, and it updates and supersedes the first version (Ahumada & Lapasset, 1995, Cat. <J/A+AS/109/375>). A new bibliographical search was made for each cluster, and the resulting information is organised into two tables. Some methodological aspects have been revised, in particular those concerning the delimitation of the area in the diagrams where the stragglers are selected. A total of 1887 blue-straggler candidates have been found in 427 open clusters of all ages, doubling the original number. The catalogued stars are classified into two categories mainly according to membership information.