Peremennye Zvezdy (Variable Stars) 43, No. 11, 2023 Received 24 November; accepted 12 December.	Article in PDF
	DOI: 10.24412/2221-0474-2023-43-121-127

Two New δ Scuti Stars in Hercules

A. Samokhvalov

Surgut, Russia, e-mail: sav@surgut.ru

1. Introduction

During observations of a field of the transient 2023lmj in Hercules (see Sokolovsky et al., 2023), I discovered two new small-amplitude  Scuti (DSCTC) stars that demonstrate multiperiodic pulsations. The new variable stars are listed in Table 1. Their coordinates were drawn from the Gaia DR3 catalog (Gaia Collaboration, 2022). None of these stars are currently contained in the AAVSO Variable Star Index (VSX). However, they are marked VARIABLE in the Gaia DR3 catalog, see Gaia Data Release 3 (Gaia DR3), Part 4, Variability (2022).

2. Observations and magnitude calibration

Our observations were carried out at the Caucasian Mountain Observatory (CMO) of M.V. Lomonosov Moscow State University, see Shatsky et al. (2020), using the 0.25-m remote controlled Ritchey-Chretien telescope, equipped with a SBIG STXL-6303e CCD camera with a filter. A total of 978 images with 600-s exposures were obtained on JD 2460120 - 2460257.

For basic reductions for dark current, flat fields, and bias, we used IRAF routines and proprietary software TheSkyX^TM by Software Bisque Inc. For photometry of new pulsating stars, we applied VaST software by Sokolovsky & Lebedev (2018). All times in this paper are expressed in terrestrial time in accordance with IAU recommendations (resolution B1 XXIII IAU GA), with heliocentric corrections applied. For magnitude calibration in band, we apply data from the Gaia DR3 catalogue. We use single, relatively bright stars, but with no saturation of pixels for our CCD camera, without close neighbors, and not demonstrating brightness variations during the time interval of our observations. Detailed information about our calibration stars is collected in Table 2. Uncertainties in the column were derives from our photometry; Gaia , , and magnitudes were drawn from the corresponding catalog. Magnitudes in the Calc. column were obtained using the equation:

which is based on table 5.9 of the Gaia Data Release 3, Documentation release 1.2
(https://gea.esac.esa.int/archive/documentation/GDR3/).

To derive periods, we use Period04 software by Lenz & Breger (2005) that implements discrete Fourier transform and is very suitable for analysis of sine-shaped light curves of multiperiodic pulsating variable stars.

3. Results

3.1. USNO-A2.0 0975-13540472

Observations of this star show rapid variations at a time scale of about with a peak-to-peak amplitude about . We searched for periodic signals in the observations using Period04 software in the frequency range between 3 and 20 cycles per day that was selected following recommendations by Breger (2000). Four apparently significant frequencies were detected; their parameters corresponding to the equation:

determined by least squares, are collected in Table 3.

Figure 1 presents the amplitude spectrum of USNO-A2.0 0975-13540472 and its theoretical light curve (solid curve) with superposed data points corresponding to individual observations. Light curve variations are easy to notice, they are reproduced with the model rather well. The finding chart based on POSS2 red plate is presented in Fig. 2.

The -filter phased light curve of USNO-A2.0 0975-13540472 with the following light elements:

is presented in Fig. 3.

3.2. USNO-A2.0 1050-12146993

Photometric measurements of this star reveal rapid variations at a time scale of about and with a peak-to-peak amplitude about . To search for periodic signals in the observations, we applied Period04 software in the frequency range between 3 and 20 cycles per day that had been selected following recommendations by Breger (2000). Three apparently significant frequencies were detected; their parameters, corresponding to Equation 2 determined by least squares, are collected in Table 4.

Figure 4 presents the amplitude spectrum of USNO-A2.0 1050-12146993 and its theoretical light curve (solid curve) with superposed data points corresponding to individual observations. Light curve variations are easy to notice, they are reproduced with the model rather well. The finding chart based on POSS2 red plate is presented in Fig. 5. The -filter phased light curve of USNO-A2.0 1050-12146993 with the following light elements:

is presented in Fig. 6.

Acknowledgements: I would like to thank N.N. Samus for helpful discussion.

References:

Breger, M., 2000, ASP Conference Series, 210, 3

Gaia Collaboration, Vallenari, A., Brown, A. G. A., et al., 2022, ArXiv:2208.00211

Lenz, P. & Breger, M., 2005, Comm. in Asteroseismology, 146, 53

Shatsky, N., Belinski, A., Dodin, A., et al. 2020, in Ground-Based Astronomy in Russia. 21st Century, ed. I. I. Romanyuk, I. A. Yakunin, A. F. Valeev, & D. O. Kudryavtsev, pp. 127-132

Sokolovsky, K., Skrotkiy, S., Potapov, N., et al. 2023, Transient Discovery Report for 2023-06-23

Sokolovsky, K. V. & Lebedev, A. A., 2018, Astron. and Computing, 22, 28

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