SSSPMJ0829-1309: A new nearby L dwarf detected in SuperCOSMOS Sky Surveys

The SuperCOSMOS Sky Surveys provide a complete coverage of the Southern sky in three passbands (photographic B_J, R and I) and at different epochs (Hambly et al. 2001a,b,c). These data are the basis for a new high proper motion survey which aims at finding extremely red nearby dwarf stars and brown dwarfs. One of the first candidates, which is relatively bright (I=16) but very red (R-I=2.8, B_J-R=3.6), was detected in the equatorial zone by its large proper motion of 0.56 arcsec/yr. Spectroscopic follow-up observations with the 2.2m telescope of the Calar Alto Observatory classified this object as L2 dwarf very similar to the first free-floating L dwarf Kelu1 also discovered in a proper motion survey by Ruiz et al. (1997). If we assume SSSPMJ0829-1309 to have the same luminosity as Kelu1, we get a distance estimate for the new L dwarf of about 12pc since it is about one magnitude brighter than Kelu1 in the SSS I and R bands. This makes SSSPMJ0829-1309 one of the nearest objects of its class, well suited for detailed investigations. We present a brief overview of all known nearby (d<20pc) southern L dwarfs and give first proper motion values for DENIS-PJ0255-47 and SDSSpJ1326-00 and an improved proper motion for LHS102B.Comment: 4 pages, 1 figure, accepted for publication in MNRAS Letter

New nearby white dwarfs from Gaia DR1 TGAS and UCAC5/URAT

Using an accurate Gaia TGAS 25pc sample, nearly complete for GK stars, and selecting common proper motion (CPM) candidates from UCAC5, we search for new white dwarf (WD) companions around nearby stars with relatively small proper motions. For investigating known CPM systems in TGAS and for selecting CPM candidates in TGAS+UCAC5, we took into account the expected effect of orbital motion on the proper motion as well as the proper motion catalogue errors. Colour-magnitude diagrams (CMDs) $M_J/J-K_s$ and $M_G/G-J$ were used to verify CPM candidates from UCAC5. Assuming their common distance with a given TGAS star, we searched for candidates that occupied similar regions in the CMDs as the few known nearby WDs (4 in TGAS) and WD companions (3 in TGAS+UCAC5). CPM candidates with colours and absolute magnitudes corresponding neither to the main sequence nor to the WD sequence were considered as doubtful or subdwarf candidates. With a minimum proper motion of 60mas/yr, we selected three WD companion candidates, two of which are also confirmed by their significant parallaxes measured in URAT data, whereas the third may also be a chance alignment of a distant halo star with a nearby TGAS star (angular separation of about 465arcsec). One additional nearby WD candidate was found from its URAT parallax and $GJK_s$ photometry. With HD 166435 B orbiting a well-known G1 star at ~24.6pc with a projected physical separation of ~700AU, we discovered one of the hottest WDs, classified by us as DA2.0$\pm$0.2, in the solar neighbourhood. We also found TYC 3980-1081-1 B, a strong cool WD companion candidate around a recently identified new solar neighbour with a TGAS parallax corresponding to a distance of ~8.3pc and our photometric classification as ~M2 dwarf. This raises the question whether previous assumptions on the completeness of the WD sample to a distance of 13pc were correct.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

ASPECT: A spectra clustering tool for exploration of large spectral surveys

We present the novel, semi-automated clustering tool ASPECT for analysing voluminous archives of spectra. The heart of the program is a neural network in form of Kohonen's self-organizing map. The resulting map is designed as an icon map suitable for the inspection by eye. The visual analysis is supported by the option to blend in individual object properties such as redshift, apparent magnitude, or signal-to-noise ratio. In addition, the package provides several tools for the selection of special spectral types, e.g. local difference maps which reflect the deviations of all spectra from one given input spectrum (real or artificial). ASPECT is able to produce a two-dimensional topological map of a huge number of spectra. The software package enables the user to browse and navigate through a huge data pool and helps him to gain an insight into underlying relationships between the spectra and other physical properties and to get the big picture of the entire data set. We demonstrate the capability of ASPECT by clustering the entire data pool of 0.6 million spectra from the Data Release 4 of the Sloan Digital Sky Survey (SDSS). To illustrate the results regarding quality and completeness we track objects from existing catalogues of quasars and carbon stars, respectively, and connect the SDSS spectra with morphological information from the GalaxyZoo project.Comment: 15 pages, 14 figures; accepted for publication in Astronomy and Astrophysic

A near-infrared variability study in the cloud IC1396W: low star-forming efficiency and two new eclipsing binaries

Identifying the population of young stellar objects (YSOs) in high extinction regions is a prerequisite for studies of star formation. This task is not trivial, as reddened background objects can be indistinguishable from YSOs in near-infrared colour-colour diagrams. Here we combine deep JHK photometry with J- and K-band lightcurves, obtained with UKIRT/WFCAM, to explore the YSO population in the dark cloud IC1396W. We demonstrate that a colour-variability criterion can provide useful constraints on the star forming activity in embedded regions. For IC1396W we find that a near-infrared colour analysis alone vastly overestimates the number of YSOs. In total, the globule probably harbours not more than ten YSOs, among them a system of two young stars embedded in a small (~10000 AU) reflection nebula. This translates into a star forming efficiency SFE of ~1%, which is low compared with nearby more massive star forming regions, but similar to less massive globules. We confirm that IC1396W is likely associated with the IC1396 HII region. One possible explanation for the low SFE is the relatively large distance to the ionizing O-star in the central part of IC1396. Serendipitously, our variability campaign yields two new eclipsing binaries, and eight periodic variables, most of them with the characteristics of contact binaries.Comment: 13 pages, 10 figures, MNRAS, in pres

The History of the Mysterious Eclipses of KH 15D II. Asiago, Kiso, Kitt Peak, Mt. Wilson, Palomar, Tautenburg and Rozhen Observatories, 1954-97

The unusual pre-main-sequence binary star named KH 15D undergoes remarkably deep and long-lasting periodic eclipses. Some clues about the reason for these eclipses have come from the observed evolution of the system's light curve over the last century. Here we present UBVRI photometry of KH 15D based on photographic plates from various observatories, ranging in time from 1954 to 1997. The system has been variable at the ~1 mag level since at least 1965. There is no evidence for color variations, with a typical limit of Delta(B-V) < 0.2 mag. We confirm some previously published results that were based on a smaller sample of plates: from approximately 1965 to 1990, the total flux was modulated with the 48-day orbital period of the binary, but the maximum flux was larger, the fractional variations were smaller, and the phase of minimum flux was shifted by almost a half-cycle relative to the modern light curve. All these results are consistent with the recently proposed theory that KH 15D is being occulted by an inclined, precessing, circumbinary ring.Comment: 10 pages, 3 figures, 3 tables, accepted for publication in Astronomical Journa

A Complete Sample of Soft X-ray Selected AGN: I. The Data

We present the optical spectra and simple statistical analysis for a complete sample of 110 soft X-ray selected AGN. About half of the sources are Narrow-Line Seyfert 1 galaxies (NLS1s), which have the steepest X-ray spectra, strongest FeII emission and slightly weaker [OIII]5007 emission than broad line Seyfert 1s (BLS1s). Kolmogorov Smirnov tests show that NLS1s and BLS1s have clearly different distributions of the X-ray spectral slope, X-ray short-term variability, and FeII equivalent widths and luminosity and FeII/H-beta ratios. The differences in the [OIII]/H-beta and [OIII] equivalent widths are only marginal. We found no significant differences between NLS1s and BLS1s in their rest frame 0.2-2.0 X-ray luminosities, rest frame 5100A monochromatic luminosities, bolometric luminosities, redshifts, and their H$\beta$ equivalent widths.Comment: Accepted for publication in AJ (scheduled for January 2004), 21 pages, 10 figures, The paper including the optical spectra and FeII subtracted spectra can be retrieved from http://www.astronomy.ohio-state.edu/~dgrupe/research/sample_paper1.htm

Galaxien-Kollisionen und das kosmische Feuerwerk der Quasare

Lange Zeiten wurden Galaxien als autarke Welteninseln angesehen. Heute wissen wir, dass wechselseitige Beeinflussungen die großen kosmischen Systeme maßgeblich prägen und spektakuläre Prozesse in deren Zentren auslösen können

A search for LSB dwarf galaxies in the M 81 group on digitally stacked Schmidt plates

We present a search for low surface brightness (LSB) dwarf galaxies in a region of 10 square degrees around M 81. The survey is based on the digital co-addition of Schmidt plates where algorithms for sub-arcsecond co-centering, quality-weighting and sigma-clipping "bad pixel" rejection are applied. The 3? surface brightness limit is ?lim = 25.6 mag/??. In a substantial fraction of the surveyed area, the detection of LSB objects is limited by "Galactic cirrus" rather than by the limiting magnitude of the stacked image. Optimum search parameters for an automated detection of dwarf galaxies are derived from simulations. The final selection of LSB dwarf candidates relies on a combination of automated detection and visual inspection. We present six new dwarf galaxy candidates with ?B(0) ? 23 mag/??. Photometric data and best fitting parameters for the exponential model are derived both for the new candidates and for some previously known LSB dwarf galaxies in the field. For the most likely new dwarf member of the M 81 group, a central surface brightness of ?B(0) = 25.4 mag/?? and a scale-length of 0.3 kpc are derived

-supported re-discovery of a remarkable weak line quasar from a variability and proper motion survey

We demonstrate that VPMS J170850.95+433223.7 is a weak line quasar (WLQ) which is remarkable in several respects. It was already classified as a probable quasar two decades ago, but with considerable uncertainty. The non-significant proper motion and parallax from the Gaia Early Data Release 3 have solidified this assumption. Based on previously unpublished spectra, we show that VPMS J170850.95+433223.7 is a WLQ at z = 2.345 with immeasurably faint broad emission lines in the rest-frame ultraviolet. A preliminary estimate suggests that it hosts a supermassive black hole of ∼109 M⊙ accreting close to the Eddington limit, perhaps at the super-Eddington level. We identify two absorber systems with blueward velocity offsets of 0.05c and 0.1c, which could represent high-velocity outflows, which are perhaps related to the high accretion state of the quasar