|ASAS image of the Kepler Field. Full resolution, 4 MB image|
Although the launch of Kepler Mission is scheduled for February 2009, the asteroseismic targets for the first year should be proposed now. In order to facilitate the selection of targets, we have observed the Kepler Field using The All Sky Automated Survey - North (ASAS - North) instruments for over a year. Then we have performed a detailed search for variablility, which resulted in detection of almost 1000 variable stars that are presented in this catalogue.
The data analyzed here were obtained in the ASAS3-North station located at Haleakala (Maui, Hawaii Islands) using two wide-field instruments, equipped with Nikkor 200mm f/2.0 lenses and Apogee AP-10, 2048x2048 CCD cameras, collecting data in two filters (V and I). The data cover roughly 500 days between July 2006 and December 2007. The resolution of ASAS images amounts to almost 15 arcsec/pixel.
The details of image processing and reductions can be found in the previous ASAS papers, e.g.:
Pojmanski, G., 1997, Acta Astronomica, 47, 467 (astro-ph:9712146),
Pojmanski, G., 2002, Acta Astronomica, 52, 397 (astro-ph: 0210283).
The variability search was carried out using the data in the intermediate aperture (diameter of 4 pixels) by means of Fourier amplitude periodogram calculated in the range between 0 and 30 d-1. All light curves and periodograms were inspected visually. The variability type was assigned taking into account the period, amplitude and/or the shape of the light curve. In total, 947 stars were selected as variable among about 250,000 searched for variability. ONLY stars that will be covered by the CCD chips of Kepler satellite were considered. The catalog does not contain variable stars that are located in the gaps between chips.
|Table 1. List of the ASAS variables in the Kepler Field.|
The catalogue is presented in a form of a Table 1. including the most important information (one row per star). The data, finding charts and additional information can be retrieved following the link which is the master ASAS identification of a star (second column of the table).
|2||Master ASAS identification (in the format of hhmmss+ddmm.m) coming from the equatorial coordinates of the object (epoch 2000.0) in the abbreviated form.|
|3||Right ascension of the object (for epoch 2000.0) [in degrees].|
|4||Declination of the object (for epoch 2000.0) [in degrees]. Right ascension and declination are given with the accuracy of 0.00001 deg for objects identified with 2MASS sources and with the accuracy of 0.0001 deg for the remaining stars. The latter means that a star is a blend and we are not sure which star of two (or more) objects is variable.|
|5||Mean V magnitude from ASAS (if V data were available).|
|6||Mean I magnitude from ASAS (if available).|
|7||V-I colour index from ASAS (if both V and I were available).|
|8||J magnitude from 2MASS All-Sky Catalog of Point Sources (Cutri et al. 2003).|
|9||J-H colour index from the 2MASS catalog.|
|10||H-K colour index from the 2MASS catalog. The entries in columns 8-10 are given only if a star was identified with a 2MASS source and the photometric quality flag was equal to A, B, C or D.|
|11|| Type of variability. The following types of variability were assigned:|
|12||The (quasi)period of variability [in days]. It is given for all periodic and quasiperiodic (QPER) stars.|
|13||Range of variability in V [in mag].|
|14|| Range of variability in I [in mag].
Note, please, that the range of variability for periodic stars was derived from phase diagrams in which the shape of the light curve was approximated by a truncated Fourier series and the outliers from such a fit were rejected. Unfortunately, this procedure usually removed points in the very deep and narrow minima of eclipsing binaries (mainly of EA type) thus leading to underestimation of derived range. On the other hand, the ranges of variability for stars identified as APER, QPER and MIRA were derived from the original light curves. In this case, the presence of outliers might lead to overestimation of the range of variability.
|15|| Remarks, notes and cross-identifications.
The column contains link 'see' if there is an entry for a given star in
this column. The stars were cross-identified with the following sources
of variability in this area of the sky:
The link on the left-hand side with ASAS ID opens a new page containing a header with sequential number, ASAS ID, type of variability and period (if available). On the right-hand side of the header the links to the first (Top), next and previous objects in the list as well as to the full table are available.
Below the header there are panels that show different plots in a form of a table with four columns and two rows with a header. The first row contains data in V, the second, in I band. The links to the original ASAS data (Data) and short information of the format (Info) are given in the first column. The second column contains light curves plotted as a function of heliocentric Julian Day. The data are shown for aperture that displays least scatter of the data, which depends on the object brightness: aperture "0" (2 pixels wide) is used for V > 14 or I > 12 and larger apertures for brighter stars, up to aperture "4" (6 pixels wide) for V < 9 or I < 7. The aperture number is also given.
For stars showing (quasi)periodic variability, the phase diagram is also shown in the third column if period was shorter than 150 days. For the remaining stars this column is blank. Finally, the fourth column contains four finding charts, centered on the variable star position. The first three images, 25x25 arcmin, were extracted from the deep (stacked) ASAS V and I images. The third image is colour-codded combination of V (green) and I images (red), that can be useful to identify blends of stars having strongly different colours (e.g. 185650+4757.2 or 190015+3934.7). The fourth image is a 5'x5' cut from the Digitized Sky Survey. Two central circles correspond to the ASAS smallest (2 pixels, 30 arcsec wide) and largest (6 pixels, 90 arcsec wide) photometric apertures.
The next table contains essentially the same entries as the main table of the catalog. The new entry is the 2MASS cross-identification (or a 'BLEND' entry if the identification was not possible due to blending). Also, the remarks/notes/cross-identifications are given explicitly here.
The last table contains the position of a star in the Kepler field (chip number and position in pixels) for four different orientations of the satellite.
The catalog we present here was intended as a support of the target selection procedure for Kepler. satellite. All remarks concerning the form of the catalog and its content are highly welcome. It is worth to note that follow-up observations of short-period variables presented in this catalogue already started in Bialkow Observatory (Poland) and Konkoly Observatory (Hungary). The main purpose of this work is to verify the nature of variability of some objects and, in the case of blended stars, checking which star is a real variable. The observers interested in observing some targets are requested to write to A.Pigulski (email@example.com). The additions, corrections and upgrades of the catalog will be logged in a file available from the main page.
We are indebet to Mr. Wayne Rosing who has kindly allocated space and
provided technical support of the LCOGT staff for ASAS-North instruments
The Faulkes Telescope North on Haleakala, Maui, Hawaii.
This project was supported by the N20300731/1328 grant from Polish Ministry of Science.