New triple-mode high-amplitude Delta Scuti variables

1 Introduction

By now, ten cases of triple-mode high-amplitude Delta Scuti variables, pulsating in the fundamental, first, and second overtone modes, were known in the Galaxy. They are V829 Aql (Handler et al. 1998), DO CMi (Wils et al. 2008), GSC 03144-00595 (Ulusoy et al. 2013), four stars in the OGLE project: OGLE-GD-DSCT-0021, OGLE-GD-DSCT-0033, OGLE-GD-DSCT-0048, and OGLE-GD-DSCT-0049 (Pietrukowicz et al. 2013); two cases, V803 Aur and V1647 Sco (detected by Khruslov 2014), and V761 Peg (detected in 2016 by F. Ferrante, announcement of August 20, 2016 in the AAVSO Variable Star Index, VSX,^[1] Watson et al. 2007 improved periods are given by Kazarovets et al. 2020). In addition, the OGLE project detected two variables of this type in the Large Magellanic Cloud, OGLE-LMC-DSCT-0927 and OGLE-LMC-DSCT-2345 (Poleski et al. 2010).

I searched for double- and multi-mode high-amplitude Delta Scuti variables using data of the All-Sky Automated Survey for Supernovae (ASAS-SN;^[2] Shappee et al. 2014, Kochanek et al. 2017). To select candidates, I used the ASAS-SN variable stars database.^[3] I chose HADS stars with scattered light curves and then analyzed observations using Deeming’s method (Deeming 1975) implemented in the WinEfk code^[4] by V. P. Goranskij.

In this article, I present a detection of four new triple-mode high-amplitude Delta Scuti variables, pulsating in the fundamental, first, and second overtone modes. In my search, along with these four variables, I detected about 300 double-mode stars pulsating in the fundamental and first overtone modes, about 20 stars pulsating in the first and second overtone modes, and several candidate HADS variables pulsating in higher overtones. These results are being prepared for publication in the Peremennye Zvezdy (Variable Stars) journal.

To improve the light elements for one of the stars (USNO-B1.0 1430-0092012, No. 1), the data of the Wide Angle Search for Planets (1SWASP;^[5] Butters et al. 2010) were used. The 1SWASP observations are available as FITS tables, which were converted into ASCII tables using the OMC2ASCII program as described by Sokolovsky (2007); we also used the SuperWASP FITS to ASCII lightcurve conversion service.^[6]

2 Results

The results are presented in Tables 1, 2, and 3. Table 1 contains general information on the studied variables: equatorial coordinates, J2000 (drawn from the Gaia DR2 catalog, Gaia Collaboration, Brown et al. 2018); star numbers from the GSC (Morrison et al. 2001), GSC2.3 (Lasker et al. 2008), USBO-A2.0 (Monet et al. 1998), and USNO-B1.0 (Monet et al. 2003) catalogs; galactic latitude b , in degrees; color indices J–K and B–V according to 2MASS (Skrutskie et al. 2006) and APASS^[7] catalogs, respectively.

Table 2 presents the light elements (period, in days, and epoch of maximum, HJD – 2457777) of individual modes (fundamental f 0 , first f 1 , and second f 2 overtone, respectively), period ratios P 1 / P 0 and P 2 / P 1 , and periods, in days, of interaction modes f 2 + f 1 and f 2 − f 1 (if they were detected).

Table 3 presents photometric parameters of the light curves: magnitudes at maximum and minimum, asymmetry parameter M – m , and semi-amplitudes of the individual oscillation modes ( A 0 , A 1 , and A 2 respectively) and the detected interaction modes ( A 2 + 1 and A 2 − 1 ).

Additional information for individual stars is presented in the following comments.

Comments for the stars:

1. Variability was detected by Pasternacki et al. (2011), BEST F2_04089. In the ASAS-SN Catalog of Variable Stars II, type HADS, P = 0.1434324 d , Jayasinghe et al. (2019). The elements were improved using the 1SWASP data.

2. Variability was detected by Jayasinghe et al. (2021) in the ASAS-SN Catalog of Variable Stars IX, type HADS, P = 0.1076939 d . A close visual pair ( d = 9 ″ ); possibly the amplitude is slightly underestimated in the ASAS-SN data. I suggest a new identification of this variable with a whiter star in the pair.

3. Variability was detected by Heinze et al. (2018). The variable is contained in the ASAS-SN Catalog of Variable Stars V, type HADS, P = 0.0761989 d (Jayasinghe et al. 2020).

4. The variability was detected by Jayasinghe et al. (2020) in the ASAS-SN Catalog of Variable Stars V, type HADS, P = 0.1768946 d . A close pair with a redder companion.

Figure 1

The light curves USNO-B1.0 1430-0092012 (No. 1).

Figure 2

GSC 04062-00915 (No. 2).

Figure 3

GSC 06574-03433 (No. 3).

Figure 4

USNO-B1.0 0257-0170560 (No. 4).

3 Conclusion

In most of the cases studied here, the period ratios P 1 / P 0 and P 2 / P 1 are typical of high-amplitude double-mode Delta Scuti stars radially pulsating in the fundamental and first overtone modes, and first and second overtone modes (Petersen & Christensen-Dalsgaard 1996). Only the P 1 / P 0 ratio for USNO-B1.0 0257-0170560 (No. 4) significantly exceeds typical values, and it is a rare case falling into the gap between two sequences.

Variations of all the four stars are dominated with the first overtone mode, A 1 > A 0 > A 2 (at least in the V band).

Figure 5 shows the Petersen diagram for all double- and multimode HADS variables detected by me. Designations in Figure 5 are the following. PL is the longer period; PS is the shorter period; open symbols are known Galactic HADS(B) stars; filled symbols are new double- and multimode variables. Circles, triangles, and squares are double, triple, and quadruple-mode variables. The red triangles correspond to the new triple-mode HADS variables announced in this article.

Figure 5

The Petersen diagram for HADS(B) stars.