We use a combination of X-shooter spectroscopy, ULTRACAM high-speed photometry and SOFI near-infrared photometry to measure the masses and radii of both components of the eclipsing post common ...envelope binaries SDSS J121258.25−012310.1 and GK Vir. For both systems, we measure the gravitational redshift of the white dwarf (WD) and combine it with light-curve model fits to determine the inclinations, masses and radii. For SDSS J1212−0123, we find an inclination of i= 85°.7 ± 0°.5, masses of M
WD= 0.439 ± 0.002 M⊙ and M
sec= 0.273 ± 0.002 M⊙, and radii R
WD= 0.0168 ± 0.0003 R⊙ and R
sec= 0.306 ± 0.007 R⊙. For GK Vir, we find an inclination of i= 89°.5°± 0°.6, masses of M
WD= 0.564 ± 0.014 M⊙ and M
sec= 0.116 ± 0.003 M⊙ and radii R
WD= 0.0170 ± 0.0004 R⊙ and R
sec= 0.155 ± 0.003 R⊙. The mass and radius of the WD in GK Vir are consistent with evolutionary models for a 50 000 K carbon-oxygen (CO) core WD. Although the mass and radius of the WD in SDSS J1212−0123 are consistent with CO core models, evolutionary models imply that a WD with such a low mass and in a short period binary must have a helium core. The mass and radius measurements are consistent with helium core models but only if the WD has a very thin hydrogen envelope (M
H/M
WD≤ 10−6). Such a thin envelope has not been predicted by any evolutionary models. The mass and radius of the secondary star in GK Vir are consistent with evolutionary models after correcting for the effects of irradiation by the WD. The secondary star in SDSS J1212−0123 has a radius ∼9 per cent larger than predicted.
Many different classes of X-ray sources contribute to the Galactic landscape at high energies. Although the nature of the most luminous X-ray emitters is now fairly well understood, the population of ...low-to-medium X-ray luminosity (LX = 1027−34 erg s-1) sources remains much less studied, our knowledge being mostly based on the observation of local members. The advent of wide field and high sensitivity X-ray telescopes such as XMM-Newton now offers the opportunity to observe this low-to-medium LX population at large distances. We report on the results of a Galactic plane survey conducted by the XMM-Newton Survey Science Centre (SSC). Beyond its astrophysical goals, this survey aims at gathering a representative sample of identified X-ray sources at low latitude that can be used later on to statistically identify the rest of the serendipitous sources discovered in the Milky Way. The survey is based on 26 XMM-Newton observations, obtained at | b | < 20 deg, distributed over a large range in Galactic longitudes and covering a summed area of 4 deg2. The flux limit of our survey is 2 × 10-15 erg cm-2 s-1 in the soft (0.5–2 keV) band and 1 × 10-14 erg cm-2 s-1 in the hard (2–12 keV) band. We detect a total of 1319 individual X-ray sources. Using optical follow-up observations supplemented by cross-correlation with a large range of multi-wavelength archival catalogues we identify 316 X-ray sources. This constitutes the largest group of spectroscopically identified low latitude X-ray sources at this flux level. The majority of the identified X-ray sources are active coronae with spectral types in the range A–M at maximum distances of ~1 kpc. The number of identified active starsincreases towards late spectral types, reaching a maximum at K. Using infrared colours we classify 18% of the stars as giants. The observed distributions of FX/FV, X-ray and infrared colours indicates that our sample is dominated by a young (100 Myr) to intermediate (600 Myr) age population with a small contribution of close main sequence or evolved binaries. We find other interesting objects such as cataclysmic variables (d ~ 0.6−2 kpc), low luminosity high mass stars (likely belonging to the class of γ-Cas-like systems, d ~ 1.5−7 kpc), T Tauri and Herbig-Ae stars. A handful of extragalactic sources located in the highest Galactic latitude fields could be optically identified. For the 20 fields observed with the EPIC pn camera, we have constructed log N(>S) − log S curves in the soft and hard bands. In the soft band, the majority of the sources are positively identified with active coronae and the fraction of stars increases by about one order of magnitude from b = 60° to b = 0° at an X-ray flux of 2 × 10-14 erg cm-2 s-1. The hard band is dominated by extragalactic sources, but there is a small contribution from a hard Galactic population formed by CVs, HMXB candidates or γ-Cas-like systems and by some active coronae that are also detected in the soft band. At b = 0° the surface density of hard sources brighter than 1 × 10-13 erg cm-2 s-1 steeply increases by one order of magnitude from l = 20° to the Galactic centre region (l = 0.9°).
The XMM-Newton serendipitous survey Rosen, S R; Webb, N A; Watson, M G ...
Astronomy and astrophysics (Berlin),
06/2016, Letnik:
590
Journal Article
Recenzirano
Odprti dostop
Context. Thanks to the large collecting area (3 x~1500 cm super(2) at 1.5 keV) and wide field of view (30' across in full field mode) of the X-ray cameras on board the European Space Agency X-ray ...observatory XMM-Newton, each individual pointing can result in the detection of up to several hundred X-ray sources, most of which are newly discovered objects. Since XMM-Newton has now been in orbit for more than 15 yr, hundreds of thousands of sources have been detected. Aims. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision of sources, greater net sensitivity for source detection, and the extraction of spectra and time series for fainter sources, both with better signal-to-noise. Thanks to these enhancements, the quality of the catalogue products has been much improved over earlier catalogues. Furthermore, almost 50% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre to produce a much larger and better quality X-ray source catalogue. Methods. The XMM-Newton Survey Science Centre has developed a pipeline to reduce the XMM-Newton data automatically. Using the latest version of this pipeline, along with better calibration, a new version of the catalogue has been produced, using XMM-Newton X-ray observations made public on or before 2013 December 31. Manual screening of all of the X-ray detections ensures the highest data quality. This catalogue is known as 3XMM. Results. In the latest release of the 3XMM catalogue, 3XMM-DR5, there are 565962 X-ray detections comprising 396910 unique X-ray sources. Spectra and lightcurves are provided for the 133000 brightest sources. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2-12 keV band counts, and four hardness ratios. With the aim of identifying the detections, a cross correlation with 228 catalogues of sources detected in all wavebands is also provided for each X-ray detection. Conclusions. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products associated with each detection and each source, it is an excellent resource for finding new and extreme objects.
We identify SDSS 011009.09+132616.1, SDSS 030308.35+005444.1, SDSS 143547.87+ 373338.5 and SDSS 154846.00+405728.8 as four eclipsing white dwarf plus main-sequence (WDMS) binaries from the Sloan ...Digital Sky Survey (SDSS), and report on follow-up observations of these systems. SDSS 0110+1326, SDSS 1435+3733 and SDSS 1548+4057 contain DA white dwarfs, while SDSS 0303+0054 contains a cool DC white dwarf. Orbital periods and ephemerides have been established from multiseason photometry. SDSS 1435+3733, with Porb= 3 h has the shortest orbital period of all known eclipsing WDMS binaries. As for the other systems, SDSS 0110+1326 has Porb= 8 h, SDSS 0303+0054 has Porb= 3.2 h and SDSS 1548+4057 has Porb= 4.4 h. Time-resolved spectroscopic observations have been obtained and the Hα and Ca ii λλ8498.02, 8542.09, 8662.14 triplet emission lines, as well as the Na i λλ8183.27, 8194.81 absorption doublet were used to measure the radial velocities of the secondary stars in all four systems. A spectral decomposition/fitting technique was then employed to isolate the contribution of each of the components to the total spectrum, and to determine the white dwarf effective temperatures and surface gravities, as well as the spectral types of the companion stars. We used a light-curve modelling code for close binary systems to fit the eclipse profiles and the ellipsoidal modulation/reflection effect in the light curves, to further constrain the masses and radii of the components in all systems. All three DA white dwarfs have masses of MWD∼ 0.4–0.6 M⊙, in line with the expectations from close binary evolution. The DC white dwarf in SDSS 0303+0054 has a mass of MWD≳ 0.85 M⊙, making it unusually massive for a post-common-envelope system. The companion stars in all four systems are M dwarfs of spectral type M4 and later. Our new additions raise the number of known eclipsing WDMS binaries to 14, and we find that the average white dwarf mass in this sample is 〈MWD〉=0.57 ± 0.16 M⊙, only slightly lower than the average mass of single white dwarfs. The majority of all eclipsing WDMS binaries contain low-mass (<0.6 M⊙) secondary stars, and will eventually provide valuable observational input for the calibration of the mass–radius relations of low-mass main-sequence stars and of white dwarfs.
We identify SDSS J121010.1+334722.9 as an eclipsing post-common-envelope binary, with an orbital period of
, containing a very cool, low-mass, DAZ white dwarf and a low-mass main-sequence star of ...spectral type M5. A model atmosphere analysis of the metal absorption lines detected in the blue part of the optical spectrum, along with the Galaxy Evolution Explorer near-ultraviolet flux, yields a white dwarf temperature of
K and a metallicity value of log Z/H =−2.0 ± 0.3. The Na i λλ8183.27, 8194.81 absorption doublet is used to measure the radial velocity of the secondary star,
, and Fe i absorption lines in the blue part of the spectrum provide the radial velocity of the white dwarf,
, yielding a mass ratio of q = 0.379 ± 0.009. Light-curve model fitting, using the Markov chain Monte Carlo method, gives the inclination angle as i = (79°.05-79°.36) ± 0°.15, and the stellar masses as
and
. Systematic uncertainties in the absolute calibration of the photometric data influence the determination of the stellar radii. The radius of the white dwarf is found to be
and the volume-averaged radius of the tidally distorted secondary is
. The white dwarf in SDSS J121010.1+334722.9 is a very strong He-core candidate.
We present follow-up spectroscopy and photometry of 11 post-common envelope binary (PCEB) candidates identified from multiple Sloan Digital Sky Survey (SDSS) spectroscopy in an earlier paper. Radial ...velocity measurements using the Na i λλ8183.27, 8194.81 absorption doublet were performed for nine of these systems and provided measurements of six orbital periods in the range Porb= 2.7– 17.4 h. Three PCEB candidates did not show significant radial velocity variations in the follow-up data, and we discuss the implications for the use of SDSS spectroscopy alone to identify PCEBs. Differential photometry confirmed one of our spectroscopic orbital periods and provided one additional Porb measurement. Binary parameters are estimated for the seven objects for which we have measured the orbital period and the radial velocity amplitude of the low-mass companion star, Ksec. So far, we have published nine SDSS PCEBs orbital periods, all of them Porb < 1 d. We perform Monte Carlo simulations and show that 3σ SDSS radial velocity variations should still be detectable for systems in the orbital period range of Porb∼ 1– 10 d. Consequently, our results suggest that the number of PCEBs decreases considerably for Porb > 1 d, and that during the CE phase the orbital energy of the binary star is may be less efficiently used to expel the envelope than frequently assumed.
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