Detached cataclysmic variables are crossing the orbital period gap

A central hypothesis in the theory of cataclysmic variable (CV) evolution is the need to explain the observed lack of accreting systems in the ~2-3 h orbital period range, known as the period gap. The standard model, disrupted magnetic braking (DMB), reproduces the gap by postulating that CVs transform into inconspicuous detached white dwarf (WD) plus main sequence (MS) systems, which no longer resemble CVs. However, observational evidence for this standard model is currently indirect and thus this scenario has attracted some criticism throughout the last decades. Here we perform a simple but exceptionally strong test of the existence of detached CVs (dCVs). If the theory is correct dCVs should produce a peak in the orbital period distribution of detached close binaries consisting of a WD and an M4-M6 secondary star. We measured six new periods which brings the sample of such binaries with known periods below 10 h to 52 systems. An increase of systems in the ~2-3 h orbital period range is observed. Comparing this result with binary population models we find that the observed peak can not be reproduced by PCEBs alone and that the existence of dCVs is needed to reproduce the observations. Also, the WD mass distribution in the gap shows evidence of two populations in this period range, i.e. PCEBs and more massive dCVs, which is not observed at longer periods. We therefore conclude that CVs are indeed crossing the gap as detached systems, which provides strong support for the DMB theory.Comment: 12 pages, 6 figures, 2 tables, accepted for publication in MNRA

The Seventh Data Release of the Sloan Digital Sky Survey

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor correction

A Multi-Wavelength View of the XMM-Newton Galactic Plane

We present an X-ray survey of the Galactic Plane conducted by the Survey Science Centre of the XMM-Newton satellite. The survey contains more than 1300 X-ray detections at low and intermediate Galactic latitudes and covering 4 deg2 well spread in Galactic longitude. From a multi-wavelength analysis, using optical spectra and helped by optical and infrared photometry we identify and classify about a fourth of the sources. The observed surface density of soft X-ray (<2 keV) sources decreases with Galactic latitude and although compatible with model predictions at first glance, presents an excess of stars, likely due to giants in binary systems. In the hard band (>2 keV) the surface density of sources presents an excess with respect to the expected extragalactic contribution. This excess highly concentrates towards the direction of the Galactic Centre and is compatible with previous results from Chandra observations around the Galactic Centre. The nature of these sources is still unknown

Entwicklung von Doppelsternsystemen nach der "common-envelope" Phase

Doppelsterne die aus einem Weißen Zwerg und einem Hauptreihenstern bestehen (WDMS-Systeme) sind ideal, um aus ihrer Beobachtung aktuelle Theorien der Doppelsternentwicklung abzuleiten. In bislang verfügbaren Stichproben sind alte Doppelsterne mit kalten Weißen Zwergen deutlich unterrepräsentiert. Wir haben eine Durchmusterung durchgeführt, die besonders der Identifizierung und Charakterisierung dieser bislang fehlenden Systeme durch Farbselektion und spektroskopische Identifikation gewidmet war. Die neue Stichprobe umfasst 277 gesicherte WDMS-Systeme und 24 weitere Kandidaten mit unsicherer kompakter Komponente. Die kombinierten Spektren wurden in ihre Komponentenspektren zerlegt und die Sternparameter bestimmt. Die so gefundene Temperarturverteilung der Weißen Zwerge zeigt ein Maximum bei deutlich niedrigeren Temperaturen als bislang verfügbare Stichproben, ist jedoch verträglich mit der Verteilung isolierter Weiß er Zwergsterne. Ebenso zeigen die Massenverteilungen einzelner Weiß er Zwerge und der neuen WDMS-Stichprobe ein Maximum bei 0.6 Sonnenmassen. Im Vergleich zu früheren enthält die neue Stichprobe einen deutlich höheren Anteil Sterne vom frühen Spektraltyp M, ist aber immer noch nicht vollständig unbiased. Es wird eine untere Grenze für die Raumdichte abhängig von der Entfernung von der galaktischen Ebene zu 0.1-2x10^-4 pc^-3 bestimmt. Die räumliche Verteilung der neuen Objekte entspricht einer Skalenhöhe von ~100-150 pc der galaktischen Scheibe. Mit Hilfe einer Radialgeschwindigkeitsanalyse spektroskopischer Daten wurden enge Doppelsterne identifiziert, die die Entwicklungsphase einer gemeinsamen Einhüllenden durchlaufen haben. Ich bestimme eine sichere untere Grenze von 13 dieser sogenannten post common envelope binaries (PCEBs) unter den WDMS-Systemen. Der Anteil der PCEBs nimmt deutlich mit abnehmender Masse der Sekundärsterne zu, insbesondere beim Übergang zu vollkonvektiven Begleitsternen. Diese Zunahme bestätigt das bislang umstrittene Modell der unterbrochenen magnetischen Bremsung, wonach der Drehimpulsverlust bei vollkonvektiven Spättypsternen deutlich reduziert werden sollte. Aus spektroskopischen und photometrischen Folgebeobachtungen wurde die Bahnumlaufzeit von 16 WDMS Doppelsternen im Bereich von Porb 2.8 Stunden bis zu 2 Tagen bestimmt und die Umlaufzeiten aller übrigen PCEBs zumindest eingeschränkt. Es wurden 7 Kandidaten mit langen und 15 Kandidaten mit kurzen Umlaufzeit gefunden. Die beobachtete Verteilung der Umlaufzeiten der PCEBs enthält wesentlich weniger langperiodische Systeme als durch Populationssynthese vorhergesagt wurde. Wahrscheinlich handelt es sich hier um einen Auswahleffekt, für Rückschlüsse auf die Effektivität der common-envelope Phase sind vollständige Stichproben notwendig. Eines der neu gefundenen Systeme zeigt Bedeckungen des Weißen Zwerges durch den Begleiter, dieses System wird in bezug auf die Sternparameter detailliert untersucht. Es wird des weiteren der Einfluss der Doppelsternnatur auf die stellare Aktivität des Sekundärsterns studiert. Der Anteil aktiver Sterne steigt zu späten Spektraltypen an, im Einklang mit Untersuchungen an Feldsternen. Der Anteil aktiver Sterne unter den frühen M-Sternen ist jedoch signifikant höher als bei den Feldsternen, was auf eine charakteristisch höheres Alter der Feldsterne zurückgeführt werden kann. Die Mehrzahl der PCEB-Systeme enthält aktive Sekundärsterne mit einer grösseren Äquivalentbreite der Halpha-Linie als bei Feldsternen gefunden wird, eine Tatsache, die zur Suche nach PCEBs unter WDMS-Systemen herangezogen werden kann.White dwarf/main sequence binaries (WDMS) are ideal systems to constrain current theories of binary star evolution. In current samples old binaries containing cold white dwarfs are significantly underrepresented. We performed a survey dedicated to identify and characterize the missing population of old white dwarf/main sequence binaries. A total of 277 white dwarf/main sequence binaries and 24 candidates were identified. We obtain their stellar parameters using a spectral decomposition method. The obtained white dwarf temperature distribution peaks at lower temperatures than previous samples but at the same temperature than the distribution of SDSS single white dwarfs. Compared to previous SDSS WDMS sample, the distribution of secondary star spectral types is slightly broader containing more early M companions, but the SEGUE WDMS population is still biased towards late spectral type secondary stars. The white dwarf mass distribution peaks at Mwd~0.6 Msun similar to that of single white dwarfs. A lower limit for the space density of 0.1-2x10^-4 pc^-3 was derived, depending on the distance from the galactic plane. The spatial distribution is in agreement with a scale-height of ~100-150 pc. From a statistical analysis of the radial velocities measured from the SDSS sub-exposures and from own spectroscopic follow-up observations we detect those binaries that have gone through a common envelope phase. I derived a lower limit to the post-common envelope binary (PCEB) fraction of WDMS binaries of ~13% . The fraction of PCEBs increases with decreasing mass of the secondary star, and has a steep increase at the boundary where the secondary star becomes fully convective. This indicates that the angular momentum loss is less efficient at later spectral types, and according to predictions of binary population synthesis studies, in agreement with the disrupted magnetic braking law. From spectroscopic and photometric follow-up observations we measured the orbital period of 16 WDMS binaries, in the range 2.8h 1 day) candidates and 15 short orbital period candidates (< 1 day). The observed orbital period distribution of PCEBs presents a sharp drop around 1 day, even though it is biased towards short orbital periods this drop might indicate a lower efficiency of the CE phase than thought. One of the systems is eclipsing, and we present an in-depth study of its stellar and binary parameters. We study the influence of binarity in the stellar activity, finding that the fraction of active stars increases with the spectral type, a result found for single field red dwarfs, though we find a higher fraction at earlier spectral types. This result can be explained by the lower age of the WDMS compared with single stars of the same spectral type. The majority of the PCEBs contain active secondaries, and at a given spectral type the EW(Ha) is higher than for wide WDMS binaries

The ASTERICS Virtual Observatory schools. Getting closer to the astronomical community

International audienceThe goal of ASTERICS WP4 (Data Access, Discovery and Interoperability) was to ensure that the ESFRI products become openly accessible via the Virtual Observatory framework to the international community. Training activities to efficiently use these new resources was identified as one of the important objectives within this work package. In this context, four Virtual Observatory (VO) schools were organised with a twofold objective:- Expose European astronomers (in particular early-career people) to the variety of VO tools and services available today so that they can use them efficiently for their own research.- Gather feedback and requirements from this intense and diverse usage.During the schools, VO experts guided the participants on the usage of VO tools through a series of tutorials built based on real life science cases. Participants also had the opportunity to develop their own science cases.One hundred and thirty-six participants from 16 different European countries attended the schools. Feedback gathered from participants demonstrated that the goals of the schools were fulfilled and that they were efficient steps forward in the process of building an astronomical VO community both within ASTERICS and beyond the project's borders across Europe

Infrared outbursts as potential tracers of common-envelope events in high-mass X-ray binary formation

Context. Classic massive binary evolutionary scenarios predict that a transitional common-envelope (CE) phase could be preceded as well as succeeded by the evolutionary stage when a binary consists of a compact object and a massive star, that is, a high-mass X-ray binary (HMXB). The observational manifestations of common envelope are poorly constrained. We speculate that its ejection might be observed in some cases as a transient event at mid-infrared (IR) wavelengths. Aims. We estimate the expected numbers of CE ejection events and HMXBs per star formation unit rate, and compare these theoretical estimates with observations. Methods. We compiled a list of 85 mid-IR transients of uncertain nature detected by the Spitzer Infrared Intensive Transients Survey and searched for their associations with X-ray, optical, and UV sources. Results. Confirming our theoretical estimates, we find that only one potential HMXB may be plausibly associated with an IR-transient and tentatively propose that X-ray source NGC 4490-X40 could be a precursor to the SPIRITS 16az event. Among other interesting sources, we suggest that the supernova remnant candidate [BWL2012] 063 might be associated with SPIRITS 16ajc. We also find that two SPIRITS events are likely associated with novae, and seven have potential optical counterparts. Conclusions. The massive binary evolutionary scenarios that involve CE events do not contradict currently available observations of IR transients and HMXBs in star-forming galaxies

VO for Everyone - Getting Ready for the 4th ASTERICS DADI VO School

4 pages, 2 figures, ADASS XXIX proceedingsInternational audienceWe present an update on the efforts of the European Virtual Observatory (EURO-VO) to inform and educate the astronomical community about Virtual Observatory (VO) tools and services. From the 20th to the 22nd of November 2018 the fourth and last Virtual Observatory school of work package 4 (DADI) of the European ASTERICS project has been taking place in Strasbourg. In the light of this event, this paper provides details on the VO-School highlighting the elements of the schools that we consider makes them a success. We present a short overview of recent developments, the current status and content, and future plans for tutorials on the Virtual Observatory

Exploring Time Domain Multi-Messenger Astronomy through the Virtual Observatory

International audienceWhat do Cepheid stars, Binary Neutron stars, Supernovae explosions and Active Galactic Nuclei have in common? They are all variable objects, although the physical processes and the associated time-scales that govern their variability can be very different (pulsations, collapse, accretion, bursts, … with characteristic time-scales from milliseconds to hundreds of years). Some events can trigger follow-up observations and a fast reaction to those events can be crucial to determining the nature of the object. To better understand the nature of these objects and the mechanism behind the source of variation a multi-wavelength and even multi-messenger approach is often needed. In 2017 for the first time there was a direct detection of gravitational waves and electromagnetic emission from colliding neutron stars. The discovery involved more than 70 ground and space based telescopes and more than 3000 astronomers. GW170817 beyond being of great relevance by its own illustrates at the highest level the need from the Time Domain Astronomy community to transmit events, collect and share information and to coordinate observations. The Virtual Observatory (VO) should match the common needs of the different scientific use cases. In this paper, we give some highlights of the work on enabling Time Domain Astronomy in the VO, and coordinating the international effort in IVOA, part of which has been done within the ASTERICS DADI package. This includes standards for spatial and temporal coverage, and Time Domain data as will be needed for Time Domain Multi-Messenger Astronomy. Other highlights include prototype visualisation tools taking into account the temporal dimension, and tools for fast cross-matching

Categorisations of object types in SIMBAD

Astronomical objects may be classified into types in many ways, and the evolution of such categorisations changes with new discoveries and progress in astrophysical understanding. The SIMBAD database contains information on astronomical objects that have been studied in the published literature, including a field that specifies astronomical object types. As a record that is derived entirely from the literature, a given astronomical object in SIMBAD may have multiple object types, and the list of object types must be maintained and updated. The SIMBAD object type list currently contains some 200 types, that are organised into a hierarchy based on astrophysical concepts. The hierarchical structure also includes relations between object types, and this facilitates searches of SIMBAD to obtain lists of all of the astronomical objects in a given category independently of the publisher or the year of publication. We will explain the organisation of astronomical object types in SIMBAD and how they may be used in queries of the SIMBAD database, and visualised on all-sky maps

Categorisations of object types in SIMBAD

International audienc