No abstract

We present a multiplicity census for a volume-complete all-sky survey of 422 stars with distances less than 25 pc and primary main-sequence effective temperatures T eff ≥ 5300 K. Very similar to previous results that have been presented for various subsets of this survey, we confirm the positive correlation of the stellar multiplicities with primary mass. We find for the F- and G-type Population I stars that 58% are non-single and 21% are in triple or higher level systems. For the old intermediate-disk and Population II stars—virtually all of G type and less massive—even two out of three sources prove to be non-single. These numbers being lower limits because of the continuous flow of new discoveries, the unbiased survey clearly demonstrates that the standard case for solar-type field stars is a hydrogen-burning source with at least one ordinary or degenerate stellar companion, and a surprisingly large number of stars are organized in multiple systems. A principal consequence is that orbital evolution, including the formation of blue straggler stars, is a potentially important issue on all spatial scales and timescales for a significant percentage of the stellar systems, in particular among Population II stars. We discuss a number of recent observations of known or suspected companions in the local survey, including a new detection of a double-lined Ba-Bb subsystem to the visual binary HR 8635.

Using robotic telescopes of the Universitätssternwarte Bochum near Cerro Armazones in Chile, we monitored the z = 0.0377 Seyfert-1 galaxy WPVS48 (2MASX J09594263-3112581) in the optical (B and R) and near-infrared (NIR, J and K s ) with a cadence of two days. The light curves show unprecedented variability details. The NIR variation features of WPVS48 are consistent with the corresponding optical variations, but the features appear sharper in the NIR than in the optical, suggesting that the optical photons undergo multiple scatterings. The J and K s emission, tracing the hot (∼1600 K) dust echo, lags the B and R variations by on average τ = 64 ± 4 days and 71 ± 5 days, respectively (restframe). WPVS48 lies on the known τ − M V relationship. However, the observed lag τ is about three times shorter than expected from the dust sublimation radius r sub inferred from the optical-UV luminosity, and explanations for this common discrepancy are searched for. The sharp NIR echos argue for a face-on torus geometry and allow us to put forward two potential scenarios: 1) as previously proposed, in the equatorial plane of the accretion disk the inner region of the torus is flattened and may come closer to the accretion disk. 2) The dust torus with inner radius r sub is geometrically and optically thick, so that the observer only sees the facing rim of the torus wall, which lies closer to the observer than the torus equatorial plane and therefore leads to an observed foreshortened lag. Both scenarios are able to explain the factor three discrepancy between τ and r sub . Longer-wavelength dust reverberation data might enable one to distinguish between the scenarios.

This paper is the second in a series describing the southern Galactic Disk Survey (GDS) performed at the Univer‐sitätssternwarte Bochum near Cerro Armazones in Chile. Haas et al. (2012, Paper I) presented the survey design and the characteristics of the observations and data. They identified ∼2200 variable stars in an area of 50 square degrees with more than 50 observations in 2011. Here we present the first complete version of the GDS covering all 268 fields with 1323 square degrees along the Galactic disk including revised data from Paper I. The individual fields were observed up to 272 times and comprise a maximum time span between September 2010 and May 2015. We detect a total of 64 151 variable sources, which are presented in a catalog including some of their properties and their light curves. A comparison with the International Variable Star Index (VSX) and All Sky Automated Survey (ASAS) indicates that 56794 of these sources are previously unknown variables. Furthermore, we present U, B, V, r ′, i ′, z ′ photometry for all sources within the GDS, resulting in a new multi‐color catalog of nearly 16×106 sources detected in at least one filter. Both the GDS and the near‐infrared VISTA Variables in the Via Lactea survey (VVV) complement each other in the overlap area of about 300 square degrees enabling future comparison studies. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We monitored the recent FUor 2MASS J06593158-0405277 (V960 Mon) since November 2009 at various observatories and multiple wavelengths. After the outburst by nearly 2.9 mag in r around September 2014 the brightness gently fades until April 2015 by nearly 1 mag in U and 0.5 mag in z. Thereafter the brightness at λ > 5000 Å was constant until June 2015 while the shortest wavelengths (U, B) indicate a new rise, similar to that seen for the FUor V2493 Cyg (HBC722). Our near-infrared (NIR) monitoring between December 2014 and April 2015 shows a smaller outburst amplitude (∼2 mag) and a smaller (0.2 -0.3 mag) post-outburst brightness decline. Optical and NIR color-magnitude diagrams indicate that the brightness decline is caused by growing extinction. The postoutburst light curves are modulated by an oscillating color-neutral pattern with a period of about 17 days and an amplitude declining from ∼0.08 mag in October 2014 to ∼0.04 mag in May 2015. The properties of the oscillating pattern lead us to suggest the presence of a close binary with eccentric orbit.