The Bochum survey of the southern Galactic disk: I. Survey design and first results on 50 square degrees monitored in 2011

Abstract

We are monitoring a 6• wide stripe along the southern Galactic disk simultaneously in the r and i bands, using a robotic 15-cm twin telescope of the Universitätsternwarte Bochum near Cerro Armazones in Chile. Utilising the telescope's 2.7• field of view, the survey aims at observing a mosaic of 268 fields once per month and to monitor dedicated fields once per night. The survey reaches a sensitivity from 10 m down to 18 m (AB system), with a completeness limit of r ∼ 15.5 m and i ∼ 14.5 m which -due to the instrumental pixel size of 2. 4 -refers to stars separated by >3 . This brightness range is ideally suited to examine the intermediately bright stellar population supposed to be saturated in deep variability surveys with large telescopes. To connect to deep surveys or to explore faint long term variables, coadded images of several nights reach a depth of ∼ 20 m . The astrometric accuracy is better than 1 , as determined from the overlap of neighbouring fields. We describe the survey design, the data properties and our procedures to derive the light curves and to extract variable stars. We present a list of ∼2200 variable stars identified in 50 square degrees with 50-80 observations between May and October 2011. For bright stars the variability amplitude A reaches down to A ∼ 0.05 m , while at the faint end variations of A > 1 m are detected. About 200 stars were known to be variable, and their amplitudes and periods -as far as determinable from our six month monitoring -agree with literature values, demonstrating the performance of the Bochum Galactic Disk Survey.

Light curves of the latest FUor: Indication of a close binary

“…The observations were obtained in the course of the Bochum Galactic Disk Survey, described in detail by Haas et al (2012) and Hackstein et al (2015). V960 Mon was monitored in the Sloan r and i filters, and since October 2014 additionally in the Johnson UBV and Sloan z filters with median sampling of 1 day.…”

Near-infrared variability in the star-forming region RCW 38

“…As discussed in Haas et al (2012), purely statistical identification of variables can lead to different biases. Compared to using the standard deviation and amplitude of the light curves, the widely used J-Index (Stetson 1996) seems to be particularly sensitive for finding variables with small amplitudes among faint noisy stars in light curves with many (>50) data points.…”

Eclipsing high-mass binaries

“…More information about the telescope and the instrument has been published by Haas et al (2012). The images were obtained simultaneously through Sloan r and i filters at 6230 Å and 7616 Å; each star was observed typically for about 40 epochs.…”

“…To improve the image quality further we resampled the frames of an original pixel size of 2.4 to a new pixel size of 0.8 using the routine SWARP (Bertin et al 2002). More information about the data reduction can be found in Haas et al (2012). Photometry was performed using an aperture radius of 4 maximizing the signal-to-noise ratio (S/N) and delivering the lowest absolute scatter for the fluxes.…”

“…Preliminary results indicate variability for about 24% of the objects (Chini et al 2013). A second sample of fainter O stars comes from the Bochum Galactic disk Survey (Haas et al 2012) where we are monitoring all stars with 10 < R, I < 15 in a strip of Δb = ±3…”