- ID:
- ivo://CDS.VizieR/J/MNRAS/415/1061
- Title:
- Variability of FBS blue stellar objects
- Short Name:
- J/MNRAS/415/1061
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method for combined calculations of magnitudes based on accurate measurements of POSS1 and POSS2 epoch plates is given. The photometric accuracy of various surveys and catalogs has been estimated and established and statistical weights for each of them have been calculated. To achieve the best possible magnitudes, weighted averaging of data from USNO-A2.0, APM, MAPS, USNO-B1.0, and GSC 2.3.2 catalogs have been used. The rms accuracy of magnitudes achieved for POSS1 is 0.184 mag for B and 0.173 mag for R and for POSS2 is 0.138 mag for B and 0.128 mag for R. We have derived the best POSS1 and POSS2 magnitudes for the FBS blue stellar objects. We have refined the transformation formulae between the POSS1 and POSS2 magnitudes and SDSS ones and standard UBV system. Using these accurate magnitudes, we have estimated the variability of the FBS blue stellar objects and revealed probable and possible variables. We have worked out methods to control and exclude accidental errors that appear in any survey. We have compared and combined our results with those given in NSVS database and obtained better candidates for variability. Having excluded variables, we have combined POSS1 and POSS2 data for the rest of objects to achieve even better magnitudes and colors; the rms being smaller than 0.1 mag both in B and R and for the B-R colors. This approach has been applied to the First Byurakan Survey blue stellar objects containing significant number of white dwarfs, cataclysmic variables, as well as extragalactic objects (quasars, Seyferts, BL Lac objects). Altogether 336 variable objects have been revealed with POSS2-POSS1 >= 3{sigma} of the errors. An electronic table of these objects is given. Candidate variables are divided into 4 classes: extreme, strong, probable and possible variables. For a more reliable sample of variable objects we excluded possible ones from the list and were left with 161 objects. Analyzing radio and X-ray properties of these objects, we have revealed their nature and re-discovered or revealed candidate AGN, CVs, WDs and other objects.
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- ID:
- ivo://CDS.VizieR/J/A+A/600/A96
- Title:
- V407 Cyg spectral variations
- Short Name:
- J/A+A/600/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The outburst of the symbiotic recurrent nova V407 Cyg in 2010 has been studied by numerous authors. On the other hand, its spectral variations in the quiescent stage have not been well studied yet. This paper is probably the first report for the relation between the pulsation of the secondary Mira variable and the temperature of the primary hot component for V407 Cyg. The spectral variation in the post-outburst stage has been monitored to study the properties of this object. In the course of this work, we found some unexpected spectral variations around the light maximum of the secondary Mira variable in 2012. The relation between the mass transfer in the binary system and the pulsation of the secondary Mira variable is studied. High- and low-resolution optical spectra obtained at the Astronomical Observatories at Asiago were used. The photometric data depend on the database of the VSNET.
- ID:
- ivo://CDS.VizieR/J/AJ/146/107
- Title:
- Velocity curves of 10 cataclysmic binaries
- Short Name:
- J/AJ/146/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on ground-based optical observations of 10 cataclysmic binaries that were discovered through their X-ray emission. Time-resolved radial velocity spectroscopy yields unambiguous orbital periods for eight objects and ambiguous results for the remaining two. The orbital periods range from 87 minutes to 9.38 hr. We also obtained time-series optical photometry for six targets, four of which have coherent pulsations. These periods are 1218s for 1RXSJ045707.4+452751, 628s for AXJ1740.2-2903, 477s for AXJ1853.3-0128, and 935s for IGRJ19267+1325. A total of seven of the sources have coherent oscillations in X-rays or optical, indicating that they are intermediate polars (DQ Herculis stars). Time-resolved spectroscopy of one object, SwiftJ2218.4+1925, shows that it is an AM Herculis star, or polar, and IGRJ19552+0044 may also be in that class. For another object, SwiftJ0746.2-1611, we find an orbital period of 9.384 hr and detect the spectrum of the secondary star. The secondary's spectral contribution implies a distance of 900 (+190, -150)pc, where the error bars are estimated using a Monte Carlo technique to account for correlated uncertainties.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A130
- Title:
- VLBI images of gamma-ray nova V407 Cygni
- Short Name:
- J/A+A/638/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 2010 March, the Large Area Telescope on board Fermi revealed a transient gamma-ray source that is positionally coincident with the optical nova in the symbiotic binary, V407 Cyg. This event marked the first discovery of gamma-ray emission from a nova. We aim to obtain resolved radio imaging of the material involved in the nova event, to determine the ejecta geometry and advance velocity directly in the image plane, and to constrain the physical conditions of the system. We observed the source with the European VLBI (Very Long Baseline Interferometry) Network in real time mode, at 1.6 and 5GHz, and the Very Long Baseline Array at 1.6, 5, and 8.4GHz. In total, we observed the source over 16 epochs, starting 20 days after the optical discovery and continuing for over six months. Milliarcsecond-scale radio emission is detected in 10/16 epochs of observations. The source is initially very dim but it later shows a substantial increase in brightness and a resolved shell-like structure 40-90 days after the optical event. The shell has a projected elliptical shape and is asymmetric in brightness and spectral index, being brighter and characterised by a rising spectrum at the south-eastern edge. We determine a projected expansion velocity of ~3500km/s in the initial phase (for an adopted 2.7kpc distance), and ~2100km/s between day 20 and 91. We also found an emitting feature about 350 mas (940AU) to the north-west, advancing at a projected velocity of ~700km/s along the polar axis of the binary. The total flux density in the VLBI images is significantly lower than that previously reported at similar epochs and over much wider angular scales with the VLA. Optical spectra convincingly demonstrated that in 2010 we were viewing V407 Cyg along the equatorial plane and from behind the Mira. Our radio observations image the bipolar flow of the ejecta perpendicular to the orbital plane, where deceleration is much lower than through the equatorial plane probed by the truncated profile of optical emission lines. The separated polar knot at 350 mas and the bipolar flow strictly resemble a similar arrangement seen in Hen 2-104, another symbiotic Mira seen equator-on that went through a large outburst ~5700yrs ago. The observed ~700km/s expansion constrains the launch date of the polar knot around 2004, during the accretion-fed active phase preceding the 2010 nova outburst.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/3241
- Title:
- White dwarfs in SDSS Stripe 82
- Short Name:
- J/MNRAS/473/3241
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Binary evolution theory predicts that accreting white dwarfs with substellar companions dominate the Galactic population of cataclysmic variables (CVs). In order to test these predictions, it is necessary to identify these systems, which may be difficult if the signatures of accretion become too weak to be detected. The only chance to identify such 'dead' CVs is by exploiting their close binary nature. We have therefore searched the Sloan Digital Sky Survey (SDSS) Stripe 82 area for apparently isolated white dwarfs that undergo eclipses by a dark companion. We found no such eclipses in either the SDSS or Palomar Transient Factory data sets among our sample of 2264 photometrically selected white dwarf candidates within Stripe 82. This null result allows us to set a firm upper limit on the space density, {rho}0, of dead CVs. In order to determine this limit, we have used Monte Carlo simulations to fold our selection criteria through a simple model of the Galactic CV distribution. Assuming a T_WD_=7500K, the resulting 2{sigma} limit on the space density of dead CVs is {rho}0<~2x10^-5^pc^-3^, where TWD is the typical effective temperature of the white dwarf in such systems.
