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Start Over Subject photometry Validation Level 2
481. BL Lac objects beyond z=1.3
ID:
ivo://CDS.VizieR/J/A+A/538/A26
Title:
BL Lac objects beyond z=1.3
Short Name:
J/A+A/538/A26
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations of the {gamma}-ray sky with Fermi led to significant advances towards understanding blazars, the most extreme class of active galactic nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac) objects, whose sample has always suffered from a severe redshift incompleteness due to the quasi-featureless optical spectra. Our goal is to provide a significant increase of the number of confirmed high-redshift BL Lac objects contained in the 2 LAC Fermi/LAT catalog.
482. BL Lacs optical light curves & X-ray prop.
ID:
ivo://CDS.VizieR/J/A+A/640/A132
Title:
BL Lacs optical light curves & X-ray prop.
Short Name:
J/A+A/640/A132
Date:
21 Oct 2021
Publisher:
CDS
Description:
It has become evident that one-zone synchrotron self-Compton models are not always adequate for very high-energy (VHE) gamma-ray-emitting blazars. While two-component models perform better, they are difficult to constrain due to the large number of free parameters. In this work, we make a first attempt at taking into account the observational constraints from very long baseline interferometry (VLBI) data, long-term light curves (radio, optical, and X-rays), and optical polarisation to limit the parameter space for a two-component model and test whether or not it can still reproduce the observed spectral energy distribution (SED) of the blazars. We selected five TeV BL Lac objects based on the availability of VHE gamma-ray and optical polarisation data. We collected constraints for the jet parameters from VLBI observations. We evaluated the contributions of the two components to the optical flux by means of decomposition of long-term radio and optical light curves as well as modelling of the optical polarisation variability of the objects. We selected eight epochs for these five objects based on the variability observed at VHE gamma rays, for which we constructed the SEDs that we then modelled with a two-component model. We found parameter sets which can reproduce the broadband SED of the sources in the framework of two-component models considering all available observational constraints from VLBI observations. Moreover, the constraints obtained from the long-term behaviour of the sources in the lower energy bands could be used to determine the region where the emission in each band originates. Finally, we attempt to use optical polarisation data to shed new light on the behaviour of the two components in the optical band. Our observationally constrained two-component model allows explanation of the entire SED from radio to VHE with two co-located emission regions.
483. BLR-less AGNs in Stripe82
ID:
ivo://CDS.VizieR/J/MNRAS/438/557
Title:
BLR-less AGNs in Stripe82
Short Name:
J/MNRAS/438/557
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the first paper in a dedicated series to study the properties of the optically-selected broad-line-region-less (BLR-less) active galactic nuclei (AGNs; with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136 676 spectroscopic objects (galaxies and quasars) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22 693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission R_AGN_>0.3 and apparent stellar lights R_ssp_>0.3. Then, using the properties of the photometry magnitude RMS (RMS) and Pearson's coefficients (R_1,2_) between two different SDSS band light curves: RMS_k_>3xRMS_Mk_ and R_1,2_>~0.8, the final 281 pure narrow line objects with true photometry variabilities are our selected reliable candidates for the BLR-less AGNs. The selected candidates with higher confidence levels not only have the expected spectral features of the BLR-less AGNs, but also show significant true photometry variabilities. The reported sample enlarges at least four times the current sample of the BLR-less AGNs, and will provide more reliable information to explain the lack of the BLRs of AGNs in our following studies.
484. 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.
485. 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.
486. 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.
487. 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.
488. 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.
489. 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.
490. Blue stellar objects in strip DE=47{deg}
ID:
ivo://CDS.VizieR/J/other/Ap/52.369
Title:
Blue stellar objects in strip DE=47{deg}
Short Name:
J/other/Ap/52.36
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is a list of 111 blue stellar objects and individual active galaxies with excess ultraviolet continuum lying within 08h-17h in {alpha} and +45{deg} +49{deg} in {delta} (1950.0). The surveyed objects are classified in terms of activity type.