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9Peremennye Zvezdy ( Variable ¡Stars) 42, No. 9, 2022 Received 24 October; accepted 2 November.
DOI: 10.24412/2221-0474-2022-42-51-59
CCD Photometry of Young Stars AS 205 (V866 Sco), V1082 Cyg, and AS 310
Ulvi Valiyev1, Sabahattin Alishov2, Nariman Ismailov 2
1 Batabat Astrophysical Observatory of Nakhichevan Branch of Azerbaijan National Academy of Sciences, Azerbaijan
2 N. Tusi Shamakhy Astrophysical Observatory of Azerbaijan National Academy of Sciences, Shamakhy region, Azerbaijan
We present the results of BVRcIc CCD photometric observations of the classical T Tauri stars AS 205 (V866 Sco), V1082 Cyg and the HAeBe star AS 310 obtained in 2016-2022. Photometric variations of the star AS 310 with a large amplitude were reliably established for the first time, they are possibly due to binarity or multiplicity of the star. The scale of the star's activity differs from a year to year. Parameters of the upgraded photometric system, currently at use at the Shamahy Observatory, are described.
1 Introduction
In most cases, the brightness of classical T Tauri stars (CTTS) varies in a complex manner (Parenago, 1954; Herbst et al., 1994; Ismailov, 2005; Grankin, 2016). It is possible that irregular disk accretion in stars of this type causes an inhomogeneity of the stellar surface, so that the star's axial rotation can provide quasi-cyclic light variations. However, in some cases, the amplitude of light variation exceeds 1 mag, and the time scale of observed variations can be quite large. Therefore, it is desirable to obtain as many photometric observations of such objects as possible in order to conduct research in each specific case. In this work, the results of photometric observations of two CTTS and one Herbig AeBe (HAeBe) star, acquired in 2016-2022, are presented.
The CTTS AS 205 A = AS 205 N (V866 Sco) is a star of the spectral type K5 in a moderately bright (V = 12m4) triple system. At an angular distance of 1.3 from AS 205 N (corresponding to «180 a.u. at the distance of 140 pc), there is a low-mass K7-M0 spectroscopic binary AS 205 S (Ghez et al., 1993; Prato et al., 2003). Two stable periods (Pi = 6.78 and P2 = 24.78) are observed in the AS 205N light curve (Artemenko et al., 2010). The P1 period is a typical one for CTTS and can be explained with the presence of cool spots on the stellar surface. The phase diagram of the P2 period shows a modulation of brightness and color, indicating the presence of an additional cool source in the system. Since AS 205 N is about 2 times brighter than AS 205 S in the V band (Herbig & Bell, 1988), the observed brightness modulation (AV = 0m25) should be attributed to the main star. From the temperature and bolometric luminosity relations (Andrews et al., 2009), the mass of AS 205 N is expected to be about 0.9M©.
Table 1: Results of photometric observations of AS 205 (V866 Sco)
JD2450000+ B JD2450000 + V JD2450000 + Rc JD2450000+ Ic
8667.2868 12.205 8667.2781 11.125 8667.2710 10.675 8667.2980 9.217
8668.2470 12.747 8668.2382 11.546 8668.2304 10.889 8668.2550 9.411
8669.2433 13.276 8669.2302 11.951 8669.2228 11.303 8669.2570 9.663
8687.2432 12.136 8687.2328 10.983 8670.3806 10.979 8687.2570 8.931
8688.2468 12.144 8688.2241 11.007 8672.3343 10.803 8688.2580 8.839
8695.2929 12.070 8695.2796 10.846 8687.2278 10.415 8695.3050 8.795
8998.3921 12.035 8700.2743 10.186 8688.2194 10.497 8700.2940 8.389
9000.3298 11.935 8712.1937 10.747 8695.2671 10.309 8712.2160 8.906
9013.3259 12.533 8998.3840 11.032 8700.2690 9.768 8998.4029 9.102
9017.2465 12.533 9000.3211 10.935 8712.1903 10.274 9000.3377 9.001
9024.2550 12.632 9013.3187 11.320 8998.3762 10.537 9024.2702 9.405
9047.3554 12.035 9014.2323 11.224 9000.3156 10.438 9047.3680 9.001
9049.2406 13.429 9017.2366 11.416 9012.3474 10.537 9049.2488 9.809
9349.3546 13.828 9019.2872 11.032 9013.3143 10.833 9349.3638 10.415
9351.3605 14.326 9024.2410 11.512 9014.2251 10.833 9351.3664 10.617
9352.3855 13.728 9047.3479 10.935 9017.2308 10.833 9352.3932 10.314
9367.2569 12.832 9049.2335 12.088 9019.2827 10.635 9367.2725 9.405
9368.2532 12.931 9349.3453 12.665 9024.2314 10.932 9368.2692 9.405
9382.3541 12.632 9351.3549 12.953 9047.3456 10.537 9382.3638 9.405
9385.3775 12.533 9352.3723 12.377 9049.2284 11.426 9385.3831 9.304
9386.3855 12.433 9367.2350 11.608 9349.3398 12.020 9386.3939 9.304
9399.2784 12.433 9368.2367 11.800 9351.3511 12.217 9399.2879 9.203
9400.2731 11.836 9382.3407 11.512 9352.3511 11.723 9400.2824 8.799
9401.2339 12.035 9385.3704 11.416 9367.2203 11.130 9401.2391 8.799
9407.2315 11.836 9386.3823 11.320 9368.2281 10.932 9407.2362 8.698
9411.3186 11.935 9399.2705 11.320 9382.3342 10.932 9411.3240 8.900
9413.2780 12.433 9400.2653 10.839 9385.3672 10.833 9412.3567 9.304
9401.2280 10.839 9386.3797 10.734 9413.2864 9.102
9407.2270 10.743 9399.2659 10.734
9411.3095 10.935 9400.2600 10.339
9412.3450 11.416 9401.2235 10.339
9413.2666 11.224 9407.2239 9411.3066 9412.3419 9413.2600 10.240 10.339 10.833 10.635
Table 2: Results of photometric observations of V 1082 Cyg
JD2450000+ V JD2450000+ B
8669.4194 13.004 8669.4249 14.197
8672.3626 12.715 8672.3681 13.799
8686.4394 13.296 8686.4448 14.547
8687.3276 12.980 8687.3333 14.140
8695.3362 13.173 8695.3509 14.500
8700.3563 13.122 8700.3699 14.369
9407.3367 12.822 9407.3424 13.933
9411.3383 13.251 9412.3779 14.552
9412.3744 13.305 9413.3411 14.385
9413.3345 13.199 9415.3452 14.315
9415.3384 13.138 9411.3441 14.524
9428.3491 13.003 9428.3574 14.188
9432.3191 12.993 9432.3275 14.134
9433.3068 13.067 9433.3149 14.237
9434.3348 13.027 9434.3431 14.179
9436.3553 12.780 9436.3641 13.858
9438.3355 13.136 9438.3417 14.322
Figure 1.
Comparison of the international BVRcIc and ShAO instrumental photometric systems. The points are approximated by straight lines, the reliability coefficient is R2 = 0.998 ± 0.001.
V1082 Cyg (HBC 728) is considered a typical CTTS, with a distance to the star of 660 pc. The V brightness of the star is 13m3. Due to its being relatively faint, this star remained poorly studied. In the catalog by Herbig & Bell (1988), its number is HBC 728. Grankin et al. (2007) found for the star an average variability amplitude of 0m828. Percy et al. (2010), mentioning the stars's photographic magnitude range 13m8 - 15m0, determined the range of its periodic variations AV < 0m3, the period being 22d. There is no accurate measurement of the star's spectral type because of its strong emission lines. Its average effective temperature is estimated as 5500 K.
The V-band brightness of the Herbig AeBe star AS 310 (HBC 284) is 12m52, and its variability is relatively poorly studied. No periodical brightness variations were detected (Percy et al., 2010). The spectral type of the star was determined as BIVe, with effective temperature at 25800 K (Hernandez et al., 2004).
2 Observations
CCD photometry of the program stars was performed at the Cassegrain focus of the 60 cm Carl Zeiss telescope of the Shamakhy Astrophysical Observatory. As a light detector, an FLI 4 x 4 k CCD camera was used. The photometer is equipped with standard
• • - - |C1 0 ! 1 • ♦ • 4 * - * • • J • • • * *|C2 • 0 - . • AS 205 ♦ * • t
• Jt •• • . • • * • , • » * • •
S • • 2* •
1* * ' * ♦
Figure 2.
The finding chart for the program star AS 205. O is the program object, S is the reference (standard) star, C1 and C2 are check stars.
BVRcIc filters. After the previous modification of the photometer (Abdullayev et al., 2012, and references therein), several of parameters of the system were improved. Since our observations were obtained using the upgraded system, this paper describes the new photometer+telescope system which is currently in use.
The telescope, with an aperture of 600 mm and equivalent focal length F = 7500 mm, has the scale in its focal plane j = 27.5" per mm. Considering that the pixel size is 9jm and the number of pixels per side is 4096, the size of the useful part of the focal plane is approximately 17' x 17'.
With the given pixel size, we get 0.247 for single-pixel resolution. Depending on the seeing, 2 x 2 or 4 x 4 binning was used, corresponding respectively to 0.49 per pixel and 0.99 per pixel. The total area covered by the camera is approximately 30', and the effective linear area in the focal plane is 17' x 17'. Dark, bias, flat-field calibration images were regularly taken during observations.
To transfer the instrumental system to the international Johnson-Cousins system, transition coefficients were determined based on observations of Landolt standards (Lan-dolt, 1992). Currently, standard star fields are listed in the European Southern Observatory (ESO) (https://www.eso.org/sci/observing/tools/standards/Landolt.html) directory. The fields with Landolt standards were selected so that the brightness of the standards located there was close to the brightness of the program stars.
Diagrams in Fig. 1 show comparison between the brightness of standard stars and
Figure 3.
The finding chart for the program star V1082 Cyg. Same designations as in Fig. 2.
the instrumental brightness measurements obtained in different bands. For each panel of Fig. 1, the corresponding transition formulas and the reliability coefficient R2 of the approximating straight line are given. As can be seen, the transition coefficients allow us to reduce the results to the international system with a high accuracy.
The formulas for converting our instrumental system to the international BVRcIc system are the following:
B = 0.996b + 0.0827, V = 0.9607w + 0.5599, Rc = 0.9886rc + 0.1563, (1)
Ic = 1.0096zc - 0.0852.
Here, the lowercase letters (right side) correspond to magnitudes in the instrumental system. When approximating the data, the reliability coefficient of passing a straight line through the data points was, on average, R2 = 0.998 ± 0.001.
All reductions of the observations were performed using the MaxIm DL software. Typical average measurement errors for individual bands are ±0m008 V, ±0.01 Rc, ±0m02 Ic, and ±0m03 B.
• *
AS 310 * 0 ■ #
• i.
# - ' #
m V ® * # # #
• m C1 • ■
■ *• • 1 • C2 • '
' 1 * ,*
• • * 0 s •
• 2* l • # '
• • •
Figure 4.
The finding chart for the program star AS 310. Same designations as in Fig. 2.
Obtained observations
Our photometric measurements performed using the differential method. In Figs. 24, finding charts of the program stars are presented. R.m.s. errors of program-star photometry were determined with respect to standard and check stars. The magnitudes of the star AS 205 were determined relative to the reference star UCAC4 357-076076 whose magnitudes in each of the filters are the following: B = 13m775, V = 12m912, R = 12m995, I = 11m808. In order to check the stability of this star and the check stars C1 and C2, their magnitudes were derived relative to each other in different combinations in the available frames, and the stars showing stability in the derived errors were selected. The selected reference star (S) UCAC4 357-076076 and the check stars C1 and C2 are shown in Fig. 2. We used the same procedure for observations of the other program stars (Figs. 3-4). The mean rms of a measurement was calculated from photometric measurements of the check stars. In different filters, the following errors were found: ±0m02 B, ±0m008 V, ±0m005 Rc, ±0m009 Ic.
The results of our photometrical observations of the program stars are collected in Tables 1-3.
Figure 5.
The light curve of the star AS 310 in the B band for 2016-2022.
3 Conclusion
Of interest is the character of variations of the HBe star AS 310, observed in 2016-2022. Figure 5 presents its light curves in the B and V bands obtained in our observations. The maximal amplitudes registered in this time interval are AB ~ 0m4, AV ~ 0m6. Remarkably, the largest amplitude was observed for AS 310 in 2018 in the V band. Unfortunately, at that time we did not observed the star in the B band as frequently as in the V band. Our observations show that, unlike other HAeBe stars, AS 310 has an unusually large amplitude of brightness variations, possibly due to the binarity or multiplicity of the star. The star's activity was different in different years of our observations. To clarify these findings, additional long-term observations of the star are needed.
References:
Abdullayev, B. I., Alekberov, I. A., Gulmaliyev, N. I., et al., 2012, Azerbaijan Astron. J., No. 4, 39
Andrews, S. M., Wilner, D. J., Hughes, A. M., et al., 2009, Astrophys. J, 700, 1502 Artemenko, S. A., Grankin, K. N., Petrov, P. P., 2010, Astron. Reports, 54, 163 Ghez, A. M., Neugebauer, G., Matthews, K., 1993, Astron. J., 106, 2005 Grankin, K. N., Melnikov, S. Yu., Bouvier, J., et al., 2007, Astron. & Astrophys., 461, 183
Grankin, K. N., 2016, Astron. Letters, 42, 314
Herbig, G. H., Bell, K. R., 1988, Lick Obs. Bull, No. 1111, 90
Herbst, W., Herbst, D., Grossman, E. J., Weinstein D., 1994, Astrophys. J., 108, 1906
Hernandez, J., Calvet, N., Briceno, C., et al., 2004, Astron. J.,127, 1682
Ismailov, N. Z., 2005, Astron. Reports, 49, 309
Landolt, A. U., 1992, Astron. J, 104, 340
Parenago, P., 1954, Publ.Sternberg Astron. Inst.,25, 222
Percy, J. R., Grynko, S., Seneviratne, R., 2010, Publ. Astron. Soc. Pacific, 122, 753 Prato, L., Greene, T. P., Simon, M., 2003, Astrophys. J., 584, 853
Table 3: Results of photometric observations of AS 310
JD2450000+ V JD2450000+ B
7569.3330 12.597 7569.3399 13.867
7569.3330 12.576 7569.3698 13.849
7569.4000 12.516 7570.3306 13.639
7570.3215 12.541 7570.3714 13.805
7570.3558 12.57 7584.2553 13.805
7584.2468 12.578 7585.2246 13.795
7585.2167 12.561 7586.3354 13.797
7586.3269 12.556 7620.1753 13.784
7620.1634 12.566 7624.1615 13.786
7620.1634 12.566 7628.1647 13.792
7624.1495 12.568 7910.2968 13.784
7626.3037 12.579 7911.2919 13.7
7628.1533 12.572 7911.3212 13.642
7910.2903 12.456 7936.2791 13.54
7911.2831 12.504 7938.3675 13.776
7911.3120 12.506 7951.3596 13.795
7936.2703 12.497 7952.2956 13.823
7938.3634 12.438 7955.1953 13.816
7951.3555 12.568 7961.2232 13.806
7952.2916 12.493 7962.2825 13.843
7955.1910 12.467 7963.2602 13.817
7961.2063 12.51 7965.2437 13.812
7962.2658 12.476 7972.2497 13.822
7963.2434 12.544 7973.2508 13.815
7996.1412 12.436 7974.2888 13.823
7973.2421 12.372 7978.1974 13.82
7974.2824 12.401 7979.1885 13.834
7977.2798 12.331 7994.2075 13.81
7978.1768 12.46 7995.1730 13.851
7979.1821 12.464 7996.1473 13.829
7994.1621 12.473 8275.3799 13.825
7995.1650 12.561 8276.3979 13.819
7996.1412 12.436 8291.3184 13.825
8275.3731 11.96 8292.2783 13.858
8276.3915 12.463 8302.3258 13.807
8285.4671 12.524 8285.4698 13.856
8291.3087 12.217 8310.3949 13.83
8292.2686 12.458 8311.3631 13.814
8302.3162 12.185 8315.3129 13.824
8306.4274 12.555 8315.3129 13.824
8309.3293 12.456 8338.2313 13.793
8310.3832 12.41 8369.2742 13.855
8311.3528 12.248 8636.3581 14
8312.3731 12.559 8637.3359 13.652
8315.3033 12.557 8649.3425 13.76
8338.2139 12.442 8655.3121 13.625
8348.3669 12.489 8660.2863 13.852
8365.1863 12.542 8669.2950 13.839
8369.2558 12.146 8687.3021 13.776
8637.3296 12.364 8688.2861 13.757
8649.3370 12.39 8689.3819 13.802
8655.2988 12.272 8695.2378 13.737
8660.2736 12.436 8700.2280 13.718
8669.2800 12.527 8712.2634 13.744
8687.2914 12.543 8759.1823 13.843
8688.2751 12.529 8771.1540 13.818
8689.3710 12.468 8991.3612 13.794
8695.2202 12.365 8992.3337 13.819
8700.2120 12.464 8998.3562 13.763
8712.2513 12.400 9000.3697 13.814
8719.3680 12.507 9012.3312 13.83
8759.1694 12.337 9017.3509 13.774
Table 3: Continued
JD2450000+ V JD2450000+ B
8771.1417 12.333 9046.3425 13.768
8991.3495 12.373 9047.3972 13.79
8992.3214 12.553 9048.4247 13.784
8998.3471 12.543 9049.3249 13.748
9000.3579 12.591 9058.3614 13.718
9012.3224 12.501 9101.2057 13.66
9017.3389 12.564 9349.3999 13.7
9046.3329 12.551 9351.3924 13.756
9047.3878 12.515 9368.3058 13.745
9048.4088 12.414 9382.3961 13.479
9049.3188 12.539 9384.4028 13.705
9058.3535 12.504 9385.4003 13.707
9101.2005 12.502 9399.2464 13.760
9351.3861 12.532 9762.2863 13.671
9368.2946 12.476
9382.3857 12.458
9384.3968 12.511
9385.3948 12.524
9399.2381 12.534
9762.2738 12.437
