|#1. Max Planck Institute for Radio Astronomy, Bonn, Germany;
#2. Astro Space Center of Lebedev Physical Institute, Moscow, Russia;
#3. Amateur astronomical society Astrogalaxy, Moscow, Russia;
#4. Odessa National University, Odessa, Ukraine
Received: 4.06.2009; accepted: 19.06.2009
(E-mail for contact: firstname.lastname@example.org)
2. MinII = 17.85.
3. Two pulsation frequencies can be identified: 16.05974 +/-0.00049 c/d, half-amplitude 0.025 +/-0.001 mag, and 14.40987 +/-0.00057 c/d, half-amplitude 0.022 +/-0.001 mag. Light elements: HJDmax(TT) = 2454866.7478 + 0.062268 x E and HJDmax(TT) = 2454874.7290 + 0.069397 x E.
4. MinII = 16.25. Unequal minima (not typical for EW eclipsing binaries) may be a result of high starspot activity.
5. MinII = 17.35.
6. 2MASS 10595715+3750203 (J = 15.385 +/-0.042, H = 15.320 +/-0.087, Ks = 15.215 +/-0.133 measured on JD 2450912.8110), infrared colors are consistent with spectral type A, typical of RR Lyrae variable stars. This is a double-mode RR Lyrae variable star with the fundamental frequency 2.10743 +/-0.00020 c/d, half-amplitude 0.161 +/-0.007 mag, and first overtone frequency 2.83538 +/-0.00014 c/d, half-amplitude 0.229 +/-0.006 mag. The first overtone to fundamental mode period ratio is 0.743. Light elements for the fundamental mode pulsation: HJDmax(TT) = 2454876.9243 + 0.47451 x E; for the first overtone: HJDmax(TT) = 2454848.0016 + 0.35269 x E.
9. 2MASS 11030886+3747491 (J = 12.604 +/-0.022, H = 12.342 +/-0.023, Ks = 12.315 +/-0.020 measured on JD 2450912.8387), infrared colors are consistent with F spectral type (Bessell & Brett 1988). Classification as an EW eclipsing binary with the light elements HJDmin(TT) = 2454875.7161 + 0.43511 x E is also possible.
10. MinII = 12.33.
11. MinII = 16.05.
12. MinII = 13.95. 13. Case A-F 716, an A-F spectral type star according to low-dispersion spectroscopy by Pesch & Sanduleak (1989) which is in agreement with 2MASS colors: 2MASS 11102180+3546502 J = 14.934 +/-0.038, H = 14.864 +/-0.059, Ks = 14.567 +/-0.093. The star is a double-mode RR Lyrae variable with the fundamental frequency 2.12227 +/-0.00016 c/d, half-amplitude 0.141 +/-0.006 mag, and the first overtone frequency 2.85296 +/-0.00011 c/d, half-amplitude 0.213 +/-0.006 mag. The first overtone to fundamental mode period ratio is 0.744, typical of double-mode RR Lyrae stars (see e.g. Wils 2009). Light elements for the fundamental mode: HJDmax(TT) = 2454847.9552 + 0.47119 x E; for the first overtone: HJDmax(TT) = 2454851.7556 + 0.35051 x E.
We present a list of variable stars discovered using remotely controlled telescopes of the Tzec Maun observatory. The telescope parameters are presented in Table 1. Table 2 presents the observation log.
Telescope D (mm) F (mm) CCD camera Location Maksutov-Newton 350 1330 SBIG ST-10E Mayhill, New Mexico, USA Takahashi FSQ 106 106 530 SBIG STL-11000M Mayhill, New Mexico, USA Takahashi TOA-150 150 1100 SBIG STL-6303 Pingelly, Western Australia Table 1. Telescopes used for observations
Magnitude scale was calibrated using:
USNO-B1.0 Telescope Filter Dates N Calibration 1034-0068308 Maksutov-Newton R 2454740 - 2454856 97 a 1035-0062360 Maksutov-Newton R 2454740 - 2454858 106 a 1416-0177809 Maksutov-Newton clear 2454853 - 2454907 277 b 1415-0175241 Maksutov-Newton clear 2454853 - 2454907 286 b 1415-0175561 Maksutov-Newton clear 2454853 - 2454907 284 b 1278-0239703 FSQ 106 clear 2454846 - 2454952 679 c 1260-0187504 FSQ 106 clear 2454846 - 2454926 662 c 1264-0188140 FSQ 106 clear 2454846 - 2454921 347 c 1277-0237737 FSQ 106 clear 2454843 - 2454926 741 c 1263-0189512 FSQ 106 clear 2454843 - 2454926 718 c 1284-0212125 FSQ 106 clear 2454843 - 2454926 638 c 1262-0188469 FSQ 106 clear 2454843 - 2454926 735 c 1257-0189164 FSQ 106,TOA-150 clear 2454846 - 2454946 814 c Table 2. Observation log
(a) R magnitudes of comparison stars in the field of PKS 0528+135 (González-Pérez et al. 2001);
(b) assuming R = 15.0 for the comparison star USNO-B1.0 1415-0175230 (05:58:08.45 +51:33:34.8, J2000; R1 = 14.77, R2 = 15.27, Monet et al. 2003);
(c) V magnitudes of the comparison stars in the field of Mrk 421 (Villata et al. 1998).
The VaST software (Sokolovsky & Lebedev 2005) was used for the preliminary data reduction and detection of variable stars. Our final lightcurve analysis was conducted using two different methods. First, all lightcurves were analyzed using the Lafler-Kinman method which has the advantage that it does not assume any particular shape of a phased lightcurve. For three variable stars which show multi-periodic behavior, the final analysis was conducted using the Discrete Fourier Transform (DFT) method implemented in the Period04 software developed by Lenz & Breger (2005). For those three stars, the lightcurve approximation with a superposition of two sine waves seems to be reasonable. The errors in frequencies and amplitudes derived from the DFT analysis were estimated with Monte Carlo simulation.
Identification with the 2MASS catalog (Skrutskie et al. 2006) is provided whenever the simultaneous infrared photometric data from this catalog may improve the variability type classification. All coordinates in this paper were taken from the USNO-B1.0 catalog (Monet et al. 2003). The finding charts are made from POSS-II red images.
It was a surprise to find two double-mode RR Lyrae variables among five RR Lyrae stars identified in a single 234' x 156' field-of-view.
This research is based on data collected with the Tzec Maun Observatory, operated by the Tzec Maun Foundation. The authors are grateful to Ron Wodaski (director of the observatory) and Donna Brown-Wodaski (director of the Tzec Maun Foundation). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the UMass/IPAC-Caltech, funded by the NASA and the NSF, the Aladin interactive sky atlas, operated at CDS, Strasbourg, France and the International Variable Star Index (VSX) operated by the AAVSO. K. Sokolovsky was supported by the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the universities of Bonn and Cologne. This research has made use of NASA's Astrophysics Data System. We would like to thank S.V. Antipin for helpful discussion of the results, V.P. Goranskij for providing his software which implements the Lafler-Kinman method and E. Angelakis for reviewing this manuscript.
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