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1Peremennye Zvezdy ( Variable ¡Stars) 44, No. 7, 2024
Received 23 September; accepted 10 October.
DOI: 10.24412/2221-0474-2024-44-78-87
2MASS J23453766+7134365, New Eclipsing Binary with a Possible Pulsating Component
A. N. Tarasenkov, S. A. Naroenkov
Institute of Astronomy of Russian Academy of Sciences, 48 Pyatnitskaya Str., Moscow 119017, Russia; [email protected]
We present our study of 2MASS J23453766+7134365, an eclipsing variable star with a possible pulsating component, from a field in Cepheus. The star exhibits V-shaped eclipses with a depth of approximately 0m25 in the V band every 2?44; secondary minima are not detected. Also, sinusoidal brightness variations are detected with an amplitude of less than 0m 1 and a period of 0d 6791. They appear and disappear quasi-periodically with a characteristic time of several days. For the study of this star, we used the archive of Astrosib RC500 telescope (Mt. Terskol observatory). We conducted follow-up observations with the RC600 telescope (Caucasian Mountain Observatory) and Astrosib RC500 telescope (INASAN Kislovodsk observatory). Also, we used photometric data from the ZTF, ASAS-SN, and TESS surveys.
1 Variability discovery of 2MASS J23453766+7134365
In 2022, a long time series of a field in Cepheus (approximate center 23h46m00s, +71°30/, J2000) was obtained using the Astrosib RC-500 telescope of Terskol observatory during photometric monitoring of program objects. A log of observations of this field is presented in Table 1. In total, we acquired 4067 measurements in the V band and 4742, in the R band.
Astrosib RC-500 is a Ritchie-Chretien narrow-field photometric telescope with the focal ratio F/8 and aperture 500 mm. It is equipped with a Fli Proline 16803 CCD camera. The camera chip size is 4096 x 4096 pixels, with the pixel size of 9 microns. When using a 36 x 36 mm CCD detector, the telescope's field of view is 30/ x 30/. The telescope is equipped with a Bessel system UBVRI filter wheel for multicolor photometry. It is installed on an Astrosib FM700 mount with worm drives. The telescope is installed as a part of the program of the Institute of Astronomy of Russian Academy of Sciences aimed at creating robotic observatories (Naroenkov & Nalivkin 2018, 2019) and operates in an automatic mode.
The telescope's field of view and long exposures used during observations of the field mentioned above made it possible to conduct variable star search in this data. Time series of archive observations were processed with the VaST software package (Sokolovsky & Lebedev 2018) to detect variable objects. We found a photometrically variable source not mentioned as a known variable in the VSX database1 or in the GCVS (Samus et al. 2017). It was identified as 2MASS J23453766+7134365 (further, 2M2345) in the 2MASS All-Sky Catalog of Point Sources (Cutri et al. 2003).
1 https://www.aavso.org/vsx/
Table 1. Observations of the field in Cepheus with Astrosib RC500-Terskol
Date Filter No. of observations
2022-09-05 V 220
2022-09-10 V 169
2022-09-11 V 197
2022-09-14 V 130
2022-09-15 V 228
2022-09-17 V 92
2022-09-19 V 532
2022-09-20 V 285
2022-09-23 V 147
2022-09-24 V 118
2022-09-27 V 253
2022-09-30 V 388
2022-10-06 V 222
2022-10-07 R 357
2022-10-11 V 227
2022-10-12 V 378
2022-10-13 V 255
2022-10-14 V 226
2022-10-25 R 346
2022-10-28 R 289
2022-10-29 R 446
2022-10-30 R 320
2022-11-01 R 210
2022-11-06 R 384
2022-11-07 R 231
2022-11-08 R 475
2022-11-10 R 381
2022-11-11 R 216
2022-11-12 R 439
2022-11-14 R 446
2022-11-15 R 202
2 Data collection and reduction
Because the target star observed in the archival dataset is significantly brighter than 2M2345, the exposures of the archival frames were too short to derive the light curve and light elements of 2M2345 with a high precision. To overcome this problem, we collected ZTF photometry (Bellm et al. 2019; Masci et al. 2019) using the SNAD ZTF viewer (Malanchev et al. 2023), ASAS-SN photometry (Shappee et al. 2014), and TESS data (Ricker et al. 2014); they were processed using the Lightkurve library algorithms (Lightkurve Collaboration, 2018). Reductions of TESS data are described in detail in Tarasenkov (2024). The light elements were determined using the WinEfk tool developed by V. P. Goranskij2. The archival light curve, folded with the elements we obtained, is presented in Fig. 1. The coordinates and parallax were taken from Gaia DR3 (Gaia Collaboration 2023).
Figure 1.
Terskol archive light curve, filter V.
We also conducted follow-up observations with the RC600 telescope of the Caucasian Mountain Observatory (Berdnikov et al. 2020) and the Astrosib RC500 telescope of the INASAN Kislovodsk Observatory (Naroenkov et al. 2024). In total, we obtained 413 measurements in the V band, 1382 measurements in the R band, along with magnitude estimates in U, B, and I. The log of our follow-up observations can be found in Table 2.
To perform photometry, we used AstroimageJ software (Collins et al. 2017). We analyzed nearby stars and selected non-variable ones, with magnitudes and color indices close to those of 2M2345, as photometric standards. The UBVRI magnitudes of standard stars were taken from APASS (Henden et al. 2012) and the Gaia DR3 Syntphot catalogue (Gaia Collaboration et al. 2023). A finding chart with comparison stars is shown in Fig. 2.
3 Stellar characteristics and evidence for pulsations
The star exhibits V-shaped eclipses with a depth of approximately 0m25 in the V band every 2e?4405; secondary minima are not detected. This indicates that eclipses are tangential, and the brightness of the secondary component may be significantly lower than that of the primary. The light elements for eclipses are: Min = 2460365.975 + 2*?4405 x E. The light curves of 2M2345, folded with these elements, are shown in Fig. 3 (TESS data) and Fig. 4 (our observations and ZTF data).
Table 2. Follow-up time series observations of 2MASS J23453766+7134365
Date Filter No. of observations Telescope
2023-11-07 R 120 RC500-Terskol
2023-11-11 R 51 RC500-Terskol
2023-11-11 V 37 RC600-CM0
2023-12-07 R 60 RC500-Kislovodsk
2024-01-03 R 18 RC500-Kislovodsk
2024-01-24 V 188 RC600-CM0
2024-01-30 R 70 RC500-Kislovodsk
2024-02-24 U 17 RC500-Kislovodsk
2024-02-24 B 17 RC500-Kislovodsk
2024-02-24 V 188 RC500-Kislovodsk
2024-02-24 R 17 RC500-Kislovodsk
2024-02-24 I 17 RC500-Kislovodsk
2024-03-03 R 90 RC500-Kislovodsk
2024-04-02 R 214 RC500-Kislovodsk
2024-04-28 R 130 RC500-Kislovodsk
2024-05-19 R 189 RC500-Kislovodsk
2024-05-22 R 90 RC500-Kislovodsk
2024-06-11 R 125 RC500-Kislovodsk
2024-06-16 R 24 RC500-Kislovodsk
2024-06-21 R 62 RC500-Kislovodsk
2024-06-23 R 122 RC500-Kislovodsk
Also, sinusoidal brightness variations are detected with an amplitude of about 0m 1 and a period of 0d6791. The ephemeris for them is Max = 2458373.245 + 0d6791 x E. These variations are visible both in ground-based observations (Fig. 5, folded RC500-Kislovodsk and ZTF data) and in TESS space mission photometry (Fig. 6, folded Sector 52 data). They appear and disappear quasi-periodically with a characteristic time of several (6-7) days. Such variations may be associated with pulsations of one of the components of the binary system caused by tidal interactions (Jayaraman et al. 2024). This effect is clearly visible in TESS light curves (Figs. 7-8) and is stable on timescales of years (Sector 17-18 data were obtained in 2019, while Sectors 78-79 were observed in 2024).
According to color-spectral type relations (Fitzgerald 1970; Ducati et al. 2001), the "integral" spectral type of the system is K2-K5.
Main properties of 2M2345 are presented in Table 3.
4 Results and conclusions
2MASS J23453766+7134365 was detected in the archive of Astrosib RC500 telescope of the Terskol observatory and identified as an eclipsing variable star with the period 24405. The primary eclipses are V-shaped with a depth of approximately 0m 25 in V band; secondary minima are not detected. Also, sinusoidal brightness variations are detected with an amplitude of less than 0m 1 and a period of 0d6791. They appear and
2 http://www.vgoranskij.net/software/WinEFengVers2015-09-08.zip
Figure 2.
The RC500-Kislovodsk field. 2MASS J23453766+713436 is marked with a green circle and signed T1, photometric comparison stars are marked with red circles and signed C2-C12.
disappear quasi-periodically, with a characteristic time from 6 to 7 days. This effect may be a consequence of pulsations of one of the components.
For further study of the star, we conducted follow-up observations with the RC600 telescope (Caucasian Mountain Observatory) and the Astrosib RC500 telescope of the INASAN Kislovodsk observatory; we also collected photometric data from the ZTF, ASAS-SN, and TESS surveys. High-quality light curves in many photometric bands were obtained, and the light elements of the system were derived. The light elements for eclipses are Min = 2460365.975 + 2.4405 x E; for sinusoidal variations, the light elements are Max = 2458373.245 + 0.6791 x E. The nature of the object is not fully understood, and it requires further research.
Acknowledgements
The authors are grateful to Drs. V. P. Goranskij and K. V. Sokolovsky for providing their software. This research has made use of the International Variable Star Index (VSX) database, operated at AAVSO, Cambridge, Massachusetts, USA. This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration 2018). The authors thank the team of the Caucasus Mountain Observatory of Moscow State University for providing observational time and Prof. N. N. Samus for fruitful discussions.
References:
Bellm, E. C., Kulkarni, S. R., Graham, M. J., et al. 2019, Publ. Astron. Soc. Pacific, 131, 018002
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
phase
Figure 3.
TESS Sector 52 light curve, folded with the eclipse period 2d4405.
Berdnikov, L. N., Belinskii, A. A., Shatskii, N. I., et al. 2020, Astron. Rep., 64, 310 Collins, K. A., Kielkopf, J. F., Stassun, K. G., et al. 2017, Astron. J., 153, article id. 77 Cutri, R. M., Skrutskie, M. F., van Dyk, S., et al. 2003, The IRSA 2MASS AH-Sky Point Source Catalog, NASA/IPAC Infrared Science Archive, http://irsa.ipac.caltech.edu/applications/Gator/ Ducati, J. R., Bevilacqua, C. M., Rembold, S. B., et al. 2001, Astrophys. J., 558, 309 Fitzgerald, M. P. 1970, Astron. & Astrophys., 4, 234
Gaia Collaboration, Vallenari, A., Brown, A. G. A., et al. 2023, Astron. & Astrophys., 674, A1
Henden, A. A., Levine, S. E., Terrell, D., et al. 2012, Journ. of the AAVSO, 40, 430
Jayaraman, R., Rappaport, S., Powell, B., et al. 2024, arXiv:2409.03815
Lightkurve Collaboration, Cardoso, J. V. d. M., Hedges, C., et al. 2018, Astrophys.
Source Code Lib., record ascl:1812.013. Malanchev, K., Kornilov, M. V., Pruzhinskaya, M. V., et al. 2023, Publ. Astron. Soc. Pacific, 135, 024503
Masci, F. J., Laher, R. R., Rusholme, B., et al. 2019, Publ. Astron. Soc. Pacific, 131, 995
Naroenkov, S. A. & Nalivkin, M. A. 2018, INASAN Sci. Rep., 2, 339 Naroenkov, S. A. & Nalivkin, M. A. 2019, INASAN Sci. Rep., 3, 87 Naroenkov, S. A., Tarasenkov, A. N., & Nalivkin, M. A., 2024, INASAN Sci. Rep., 9, 6 Paegert, M., Stassun, K. G., Collins, K. A., et al. 2021, arXiv:2108.04778 Ricker, G. R., Winn, J. N., Vanderspek, R., et al. 2014, Proc. of the SPIE, 9143, 15 Samus, N. N., Kazarovets, E. V., Durlevich, O. V., et al. 2017, Astron. Rep., 61, 80 Shappee, B., Prieto, J., Stanek, K. Z., et al. 2014, American Astron. Soc., AAS Meeting 223, id.236.03
Sokolovsky, K. V. & Lebedev, A. A. 2018, Astron. & Computing, 22, 28 Tarasenkov, A. N. 2024, INASAN Sci. Rep., in preparation
Figure 4.
Astrosib RC500-Kislovodsk and ZTF light curves, folded with the light elements Min = 2460365.975 + 2d4405 x E.
Figure 5.
Astrosib RC500-Kislovodsk and ZTF light curves, folded with light elements Max = 2458373.245 + 0d6791 x E. Eclipses are excluded.
-0.2 0.0 0.2 0.4 0.6 O.a 1.0 1.2
phase
Figure 6.
TESS Sector 52 light curve in pulsation-active state, folded with the period 0d6791. Eclipses are excluded.
Table 3. Properties of 2MASS J23453766+7134365
Parameter Value Source
RA J2000 23h45m37S67 Gaia DR3 (Gaia Collaboration et al. 2023)
DEC J2000 71°34' 36"36 Gaia DR3 (Gaia Collaboration et al. 2023)
Parallax, mas 0.6360 ± 0.0158 Gaia DR3 (Gaia Collaboration et al. 2023)
Orbital period 2d4405 This work
Pulsation period 0d 6791 This work
U magnitude 16m03 ± 0m32 This work
B magnitude 15m67 ± 0m07 This work
V magnitude 14m78 ± 0m08 This work
R magnitude 14m23 ± 0m03 This work
I magnitude 13m70 ± 0m02 This work
J magnitude 12m918 ± 0.025 2MASS (Cutri et al. 2003)
H magnitude 12m600 ± 0m028 2MASS (Cutri et al. 2003)
K magnitude 12m473 ± 0m025 2MASS (Cutri et al. 2003)
Luminosity, LSun 7.72 TIC v8.2 (Paegert et al. 2021)
H ^
H rro"
cc
rr> R
Crq
cr
O
c
<
ca
TESS differential magnitude
TESS differential magnituce
TESS differential magnitude
TESS Sector 78
JD - 2457000 TESS Sector 79
3455 3460 3465 3470 3475 3480
JD- 2457000
Figure 8.
TESS lightcurves of 2M2345, Sectors 78 and 79.
