P. Guillout

The XMM-Newton serendipitous survey - VII. The third XMM-Newton serendipitous source catalogue

© ESO, 2016.Context. Thanks to the large collecting area (3 × ∼1500 cm2 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 565 962 X-ray detections comprising 396 910 unique X-ray sources. Spectra and lightcurves are provided for the 133 000 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.

A spectroscopic survey of the youngest field stars in the solar neighbourhood - I. The optically bright sample

Aims. We present the first results of an ambitious ground-based observation programme conducted on 1–4 m class telescopes. Our sample consists of 1097 active and presumably young stars, all of them being optical (Tycho Catalogue) counterparts of ROSAT AllSky Survey X-ray sources in the northern hemisphere. In this paper, we concentrate on the optically brightest (VT 9. m 5) candidates (704 objects). We acquired high-resolution optical spectroscopy in the Hα and/or lithium spectral regions for 426 of such stars without relevant data in the literature. We describe the star sample and the observations and we start to discuss the physical properties of the investigated stars. Methods. We used a cross-correlation technique and other tools developed by us to derive accurate radial and rotational velocities and to perform an automatic spectral classification for both single stars and double-lined systems. The spectral subtraction technique was used to derive chromospheric activity levels and lithium abundances. We estimated the fraction of young single stars and multiple systems in stellar soft X-ray surveys and the contamination by more evolved systems, like RS CVn binaries. We classified stars on the basis of their lithium abundance and give a glimpse of their sky distribution. Results. The sample appears to be a mixture of quite young Pleiades-like and Hyades-like stars plus an older lithium-poor population probably born within the last 1–2 Gyr. Seven stars with a lithium abundance compatible with the age of IC 2602 (about 30 Myr) or even younger were detected as well, although two appear to be lithium-rich giants.The discovery of a large number of highly or moderately lithium-rich giants is another outcome of the present survey. Conclusions. The contamination of soft X-ray surveys by old systems in which the activity level is enhanced by tidal synchronisation is not negligible, especially for K-type stars. Five stars with lithium content close to the primordial abundance are probably associated with already known moving groups in the solar neighbourhood. Some of them are good post-T Tauri candidates according to their positions in the HR diagram.

The XMM-Newton SSC survey of the Galactic plane

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 = 10 27−34 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| 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 ◦ ).

Reliable probabilistic determination of membership in stellar kinematic groups in the young disk

Context. Over the last century, the overdensities in the velocity distributions of nearby stars were attributed to stellar kinematic groups or moving groups. Although their reality was initially questioned, their existence is now supported by a confluence of evidence. nAims. To pursue investigations, quantitative methods should be clearly defined to identify new stars belonging to these groups. Here, we present two probabilistic methods to determine the likelihood of kinematic membership for possible candidates in five of the known young stellar kinematic groups – namely, Pleiades, IC 2391, Castor, Ursa Major, and Hyades – in which all are younger than 650 Myr. Methods. We tried different methods to handle kinematic data of their known members.We succeeded in developing two independent procedures able to identify new candidates of these five stellar stream. We tested the robustness of our two approaches by means of extensive Monte Carlo simulations. nResults. Our methods are consistent with one another in more than 90% of cases and for almost all the stellar kinematic groups under scrutiny. The IC2391 supercluster is an exception. Applying our statistical methods to a large sample of young low-mass stars, we confirmed almost all the likely members and good candidates of these stellar streams. We also proposed 39 additional candidates based on the agreement and the high likelihood of age and kinematic membership. nConclusions. These probabilistic methods are very powerful to reliably identify new candidate members of young stellar kinematic groups. However, the kinematic criteria alone are not sufficient to distinguish between coeval stars that are evaporated from open clusters and other field stars trapped by dynamical processes generated by galactic perturbations. The identification of stars belonging to the remnant of a past star-forming event can be possible with the help of additional information, such as indicators of chromospheric activity, age proxies (lithium abundance), and chemical composition.

Masses of the components of SB2 binaries observed with Gaia - I. Selection of the sample and mass ratios of 20 new SB2s discovered with Sophie

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the Sophie spectrograph at the Haute-Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient finally to obtain the masses of the components with relative errors as small as 1 per cent when the astrometric measurements of Gaia are taken into account. Simultaneously, the luminosities of the components in the Gaia photometric band G will also be obtained. Our observation program started with 200 SBs, including 152 systems that were only known as single-lined. Thanks to the high efficiency of the Sophie spectrograph, an additional component was found for 25 SBs. After rejection of five multiple systems, 20 new SB2s were retained, including eight binaries with an evolved primary, and their mass ratios were derived. Our final sample contains 68 SB2s, including two late-type giants and 10 other evolved stars.

Discovery of “isolated” co-moving T Tauri stars in Cepheus

Context. During the course of a large spectroscopic survey of X-ray active late-type stars in the solar neighbourhood, we discovered four lithium-rich stars packed within just a few degrees on the sky. Although located in a sky area rich in CO molecular regions and dark clouds, the Cepheus-Cassiopeia complex, these very young stars are projected several degrees away from clouds in front of an area void of interstellar matter. As such, they are very good isolated T Tauri star candidates. Aims. We present optical observations of these stars conducted with 1-2 m class telescopes. We acquired high-resolution optical spectra as well as photometric data allowing us to investigate in detail their nature and physical parameters with the aim of testing the runaway and in-situ formation scenarios. Their kinematical properties are also analyzed to investigate their possible connection to already known stellar kinematic groups. Methods. We use the cross-correlation technique and other tools developed by us to derive accurate radial and rotational velocities and perform an automatic spectral classification. The spectral subtraction technique is used to infer chromospheric activity level in the Hα line core and clean the spectra of photospheric lines before measuring the equivalent width of the lithium absorption line. Results. Both physical (lithium content, chromospheric, and coronal activities) and kinematical indicators show that all stars are very young, with ages probably in the range 10-30 Myr. In particular, the spectral energy distribution of TYC4496-780-1 displays a strong near-and far-infrared excess, typical of T Tauri stars still surrounded by an accretion disc. They also share the same Galactic motion, proving that they form a homogeneous moving group of stars with the same origin. Conclusions. The most plausible explanation of how these isolated T Tauri stars formed is the in-situ model, although accurate distances are needed to clarify their connection with the Cepheus-Cassiopeia complex. The discovery of this loose association of isolated T Tauri stars can help to shed light on atypical formation processes of stars and planets in low-mass clouds.

Masses of the components of SB2s observed with Gaia -- II. Masses derived from PIONIER interferometric observations for Gaia validation

In anticipation of the Gaia astrometric mission, a sample of spectroscopic binaries is being observed since 2010 with the Spectrograph pour lObservation des PHenomenes des Interieurs stellaires et des Exoplanetes (SOPHIE) spectrograph at the Haute-Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 per cent when combined with Gaia astrometric measurements. In order to validate the masses derived from Gaia, interferometric observations are obtained for three SB2s in our sample with F-K components: HIP 14157, HIP 20601 and HIP 117186. The masses of the six stellar components are derived. Due to its edge-on orientation, HIP 14157 is probably an eclipsing binary. We note that almost all the derived masses are a few per cent larger than the expectations from the standard spectral type-mass calibration and mass-luminosity relation. Our calculation also leads to accurate parallaxes for the three binaries, and the Hipparcos parallaxes are confirmed.

Masses of the components of SB2 binaries observed with Gaia – III. Accurate SB2 orbits for 10 binaries and masses of HIP 87895

In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the Spectrographe pour lObservation des PHenomenes des Interieurs Stellaires et des Exoplanetes spectrograph at the Haute-Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 per cent when the astrometric measurements of Gaia are taken into account. In this paper, we present the results from five years of observations of 10 SB2 systems with periods ranging from 37 to 881 d. Using the todmor algorithm, we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the components are then obtained with an accuracy better than 1.2 per cent for the 10 binaries. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 87895 with an accuracy of 0.98 and 1.2 per cent, respectively.

The X-ray source content of the XMM-Newton Galactic plane survey

We report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic Plane Survey of Hands et al. (2004). In addition to photometric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6m, we used cross-correlations with the 2XMMi, USNO-B1.0, 2MASS and GLIMPSE catalogues to progress the identification process. Active coronae account for 16 of the 30 positively or tentatively identified X-ray sources and exhibit the softes t X-ray spectra. Many of the identified hard X-ray sources are associated with massive stars, possibly in binary systems and emitting at intermediate X-ray luminosities of 10 32−34 erg s −1 . Among these are

New triple systems in the RasTyc sample of stellar X-ray sources ,,

Context. During the study of a large set of late-type stellar X-ray sources, we discovered a high fraction of multiple systems. Aims. In this paper we investigate the orbital elements and kinematic properties of three new spectroscopic triple systems, along with the spectral types and astrophysical parameters (Teff ,l ogg, v sini ,l ogN(Li)) of their components. Methods. We conducted follow-up optical observations of these systems, both photometric and spectroscopic ones at high resolution. We used a synthetic approach and the cross-correlation method to derive most of the stellar parameters. Results. We estimated reliable radial velocities and deduced the orbital elements of the inner binaries. The comparison of the observed spectra with synthetic composite ones, obtained as the weighted sum of three spectra of non-active reference stars, allowed us to determine the stellar parameters for each component of these systems. We found all are only composed of main sequence stars. Conclusions. These three systems are certainly stable hierarchical triples composed of short-period inner binaries plus a tertiary component in a long-period orbit. From their kinematics and/or lithium content, these systems turn out to be fairly young.