Peremennye Zvezdy

Peremennye Zvezdy (Variable Stars) 34, No. 3, 2014

Received 3 October; accepted 14 November.

Article in PDF

New Double-Mode RR Lyrae Variables

A. V. Khruslov

Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia; e-mail: khruslov@bk.ru


We present a new study of 28 known RR Lyrae variable stars. We analyzed all observations available for these stars in the Catalina Surveys, LINEAR, Northern Sky Variability Survey, and SuperWASP online public archives using the period-search software developed by Dr. V.P. Goranskij for Windows environment. According to these data, the stars are double-mode RR Lyrae variables, pulsating in the first-overtone and fundamental modes.

1. Introduction

According to the International Variable Star Index (VSX, AAVSO), about 600 double-mode RR Lyrae variable stars are currently known in our Galaxy, usually pulsating in the fundamental and first overtone radial modes (most of them, outside globular clusters). During the recent years, automated data surveys resulted in a considerable progress in the identification of stars of this type. Wils (2010) reported seven new RR(B) stars from WASP data. About 90 RR(B) stars in the bulge of our Galaxy were found in the OGLE project (Soszynski et al. 2011). In the Catalina Surveys Periodic Variable Star Catalog (Drake et al. 2014), results are presented for 502 RR(B) stars, at least 300 of them previously unknown. Then, a discovery of 59 new Galactic double-mode RR Lyrae stars found in the LINEAR survey data (a small part of them were found earlier by other authors) was reported by Poleski (2014). The author of the present paper, with his co-authors, earlier discovered 28 double-mode RR Lyrae variable stars, pulsating in the fundamental and first overtone radial modes ( Khruslov 2007, 2010, 2011, 2012a, 2012b; Khruslov, Huemmerich, and Bernhard 2013; Antipin and Khruslov 2013; Huemmerich and Khruslov 2014).

In this article, I present the discovery of 28 more double-mode RR Lyrae variable stars, pulsating in the first-overtone and fundamental modes.

2. Results

I studied 28 known RR Lyrae variable stars, analyzing all observations available for them in the Catalina Surveys (Drake et al. 2009), LINEAR (Sesar et al. 2011), Northern Sky Variability Survey (NSVS , Wozniak et al. 2004), and SuperWASP (Butters et al. 2010) online public archives using the period-search software developed by Dr. V.P. Goranskij for Windows environment. According to these data, the variables are double-mode RR Lyrae variables, pulsating in the first-overtone and fundamental modes.

Light curves, finding charts, and data (CSS, SSS, MLS, LINEAR, NSVS, SWASP) are available online in the html version of this paper as a zip-archive. The light curves are given in the format displayed in Fig. 1. Top panels present data folded with the fundamental-mode and first overtone periods. Bottom panels show the same curves after prewhitening the other oscillation (if the frequencies and were excluded, it is also noted). These light curves are given for all data series. In three cases (No. 16, 19, 20), the data from LINEAR and Catalina surveys could not be represented with a unified system of light elements, probably indicating that both periods, and , vary.

Fig. 1. The light curve of GSC 0923-00144 (No. 18).

Along with the light curves, we present power spectra of the RR Lyrae variables, for the raw data and after subtraction of the first-overtone (or fundamental mode) oscillations, as is shown in Fig. 2. The structure of the power spectra shows that the secondary periods are real.

Their period ratios, , are typical of radially pulsating double-mode RR Lyrae stars. The Petersen diagram for double-mode RR Lyrae variables of this article is displayed in Fig. 3.

Fig. 2. The power spectra of GSC 0923-00144 (No. 18) for the frequencies and .

Fig. 3. The Petersen diagram for the program double-mode RR Lyrae stars.

Information on the studied stars is presented in Tables 1-4. Table 1 contains numbers from the GSC and USNO-B1.0 catalogs; equatorial coordinates (J2000); type and period previously known for the star, according to references from the last column, explained below the table. The tabulated coordinates of the variables were drawn from either the GSC2.3 (Lasker et al. 2008; star No. 1 in this paper) or 2MASS catalogs (Skrutskie et al. 2006).

Table 1.

No. Name Coordinates (J2000) Type , days Ref
           
1 USNO-B1.0 1344-0191047 0744 5485 +442909 6 RRAB 04827138 1
2 USNO-B1.0 1315-0208615 09 38 03.96 +41 33 45.2 RRC 0.358592 2
3 USNO-B1.0 1338-0210776 09 59 38.04 +43 52 45.6 RRAB 0.4845666 1
4 USNO-B1.0 1336-0219968 10 54 18.77 +43 40 37.8 RRC 0.370803 2
5 USNO-B1.0 0738-0239220 11 14 36.57 -16 10 46.1 RRC 0.388355 2
6 GSC 5512-01099 11 25 21.23 -11 16 10.3 RRC 0.35973 3
7 USNO-B1.0 1349-0226600 11 33 51.94 +44 57 39.9 RRC 0.353188 2
8 USNO-B1.0 1102-0220937 12 47 46.30 +20 15 48.0 RRC 0.384393 2
9 USNO-B1.0 1329-0290328 12 50 17.77 +42 57 29.8 RRC 0.356830 2
10 USNO-B1.0 0863-0260489 13 16 41.33 -03 36 14.6 RRC 0.417676 2
11 GSC 0897-00784 13 19 46.77 +14 40 21.8 RRAB 0.460444 2
12 USNO-B1.0 1161-0225607 13 56 45.27 +26 06 41.0 RRC 0.397025 2
13 USNO-B1.0 1017-0252244 14 24 54.23 +11 47 45.2 RRAB 0.465064 2
14 USNO-B1.0 1121-0267760 14 25 47.22 +22 10 08.6 RRC 0.400458 2
15 USNO-B1.0 1226-0288064 14 36 49.56 +32 39 50.8 RRAB 0.4935225 1
16 USNO-B1.0 1100-0231107 14 40 18.08 +20 01 32.0 RRC 0.421228 2
17 USNO-B1.0 1295-0254008 14 53 55.16 +39 32 21.1 RRC 0.354983 2
18 GSC 0923-00144 15 13 07.59 +12 08 03.6 RRC 0.404021 2
19 USNO-B1.0 1265-0234869 15 46 19.18 +36 34 05.2 RRC 0.413950 2
20 USNO-B1.0 1039-0242114 15 49 41.38 +13 59 35.6 RRC 0.444205 2
21 USNO-B1.0 1088-0244594 15 54 04.37 +18 51 20.6 RRC 0.358311 2
22 USNO-B1.0 1182-0267691 16 01 28.46 +28 15 53.4 RRC 0.411701 2
23 USNO-B1.0 1023-0310699 16 08 25.22 +12 19 08.4 RRC 0.366803 2
24 USNO-B1.0 1084-0260951 16 24 27.51 +18 24 49.9 RRC 0.417560 2
25 USNO-B1.0 1381-0302066 16 39 13.41 +48 11 02.8 RRC 0.377389 2
26 USNO-B1.0 0667-0901820 19 52 26.89 -23 17 54.3 RRC: 0.33662 4
27 USNO-B1.0 0820-0768849 21 17 23.39 -07 59 10.9 RRAB 0.4679295 1
28 USNO-B1.0 0680-1002029 21 17 28.18 -21 56 09.0 RR: - 5
           

References in Table 1:

1. Drake et al. (2013)

2. Palaversa et al. (2013)

3. Hadon, VS-COMPAS team, 2012

( http://www.vs-compas.belastro.net/stars/by/type/RRC )

4. Otero, International Variable Star Index, 2014

5. Keller et al. (2008)

Table 2 presents identification numbers for the LINEAR database, other data used in the analysis, magnitude in the maximum and minimum in the Catalina surveys and LINEAR photometric systems.

Table 2. Data.

No. LINEAR ID Other data CSS magnitude LINEAR magnitude
         
1 - CSS 178-188 -
2 16982312 CSS 16.30-17.07 1640-1720
3 17701631 CSS 16.29-17.11 16.38-17.18
4 23389584 CSS 15.26-15.77 15.35-15.87
5 851716 CSS, SSS 15.86-16.65 15.93-16.60
6 - CSS, SSS, NSVS 13.32-13.98 -
7 1643135 CSS 16.13-16.84 16.22-17.17
8 4435791 CSS 16.29-16.86 16.37-16.94
9 7892817 CSS 15.75-16.39 15.82-16.49
10 8854060 CSS, MLS 16.59-17.26 16.6-17.3
11 8658610 CSS 13.62-14.41 13.75-14.54
12 10278022 CSS 16.18-16.76 16.18-16.84
13 11697185 CSS 15.56-16.38 15.71-16.46
14 11763086 CSS 15.74-16.35 15.89-16.46
15 12199470 CSS 15.18-15.95 15.33-16.03
16 12432893 CSS 16.13-16.74 16.29-16.90
17 12896695 CSS 15.47-16.05 15.63-16.39
18 13754273 CSS 13.69-14.28 13.87-14.46
19 15450888 CSS 15.63-16.25 15.81-16.35
20 15269598 CSS 15.96-16.61 16.07-16.72
21 15708768 CSS 15.75-16.29 15.67-16.39
22 16182003 CSS 15.04-15.62 15.18-15.73
23 16456815 CSS 15.25-15.86 15.45-15.98
24 18255554 CSS 14.67-15.23 14.80-15.27
25 18861334 CSS 15.83-16.53 15.93-16.68
26 - SSS, 1SWASP 14.82-15.35 -
27 - CSS 14.94-15.74 -
28 - CSS 15.35-15.92 -
         

Light elements of all oscillations: the first-overtone period , the fundamental period , the first-overtone and fundamental mode epoch of maxima, period ratios , periods of the frequencies () and () are collected in Table 3.

Table 3. Light elements.

No. , d , d Epoch, JD Epoch, JD , d , d
               
1 0.360108 0.482702 2455000.713 2455000.795 0.7460 - -
2 0.358595 0.481662 2454500.245 2454500.100 0.7445 0.205560 -
3 0.360565 0.484580 2455000.700 2455000.535 0.7441 0.206736 1.4089
4 0.370794 0.497336 2455000.260 2455000.137 0.7456 - -
5 0.388360 0.521023 2454500.080 2454500.500 0.7454 0.222508 -
6 0.359729 0.483101 2455000.766 2455000.790 0.7446 - -
7 0.353195 0.474709 2454500.329 2454500.156 0.7440 0.202515 1.3798
8 0.384402 0.515253 2454500.205 2454500.293 0.7460 0.220153 1.51369
9 0.356830 0.479250 2454500.360 2454500.395 0.7446 - -
10 0.417684 0.559293 2455000.120 2455000.525 0.7468 - -
11 0.341883 0.460448 2454500.333 2454500.397 0.7425 0.1962004 1.3277
12 0.397031 0.532235 2454500.146 2454500.410 0.7460 - -
13 0.345662 0.465042 2454500.220 2454500.354 0.7433 0.198282 1.34650
14 0.400452 0.536540 2454500.400 2454500.100 0.7464 - -
15 0.367380 0.493517 2455000.602 2455000.795 0.7444 0.210603 -
16 0.421213 0.564890 2455000.410 2455000.120 0.7457 0.241131 -
17 0.354990 0.476987 2454500.125 2454500.326 0.7442 - -
18 0.404023 0.541556 2454500.400 2454500.150 0.7460 0.231394 1.59105
19 0.413934 0.554870 2455000.075 2455000.135 0.7460 0.237077 1.62964
20 0.444237 0.596277 2455000.088 2455000.086 0.7450 - -
21 0.358319 0.481733 2454500.260 2454500.385 0.7438 0.205477 -
22 0.411690 0.551550 2454500.272 2454500.353 0.7464 - -
23 0.366799 0.491922 2454500.223 2454500.168 0.7456 0.210121 1.44205
24 0.417557 0.559638 2454500.065 2454500.450 0.7461 0.239133 1.64475
25 0.377393 0.506715 2454500.070 2454500.505 0.7448 - -
26 0.33662 0.45389 2454150.080 2454150.203 0.7416 0.193312 -
27 0.347610 0.467934 2455000.820 2455000.851 0.7429 0.1994484 1.35183
28 0.410838 0.550510 2455000.847 2455000.720 0.7463 - -
               

Table 4 presents semi-amplitudes of all the oscillations, separately for Catalina surveys and LINEAR data: semi-amplitudes of first-overtone () and fundamental mode () oscillations, for the () and () frequencies. Asterisks mark the amplitudes based on other data, as explained in Comments, also containing additional information about some of the stars.

Table 4. Semi-amplitudes.

No. CSS magnitude LINEAR magnitude
 
                 
1 0.096 0.240 - - - - - -
2 0.173 0.114 0.053 - 0.145 0.112 - -
3 0.148 0.135 0.052 0.037 0.219 0.164 - -
4 0.182 0.034 - - - - - -
5 0.163 0.132 0.046 - 0.208 0.064 - -
6 0.183 0.082 - - 0.127* 0.049* - -
7 0.156 0.104 0.032 0.041 0.113 0.065 - -
8 0.143 0.058 0.030 0.021 0.153 0.072 0.035 -
9 0.189 0.100 - - 0.166 0.085 - -
10 0.162 0.050 - - - - - -
11 0.183 0.170 0.075 0.029 0.145 0.158 0.058 0.021
12 0.159 0.045 - - 0.150 0.057 - -
13 0.149 0.166 0.063 0.037 0.165 0.116 0.081 -
14 0.166 0.070 - - 0.141 0.065 - -
15 0.141 0.122 0.049 - 0.163 0.114 0.046 -
16 0.137 0.063 0.025 - 0.148 0.055 - -
17 0.150 0.080 - - 0.159 0.109 - -
18 0.146 0.065 0.032 0.026 0.167 0.076 - -
19 0.173 0.069 0.036 0.022 0.132 0.057 0.037 -
20 0.146 0.103 - - 0.164 0.066 - -
21 0.164 0.052 0.023 - 0.172 0.063 - -
22 0.177 0.065 - - 0.141 0.058 - -
23 0.177 0.059 0.022 0.025 0.166 0.048 - -
24 0.139 0.055 0.023 0.017 0.154 0.038 - -
25 0.167 0.132 - - 0.150 0.099 - -
26 - - - - 0.035* 0.015* 0.007* -
27 0.156 0.155 0.057 0.036 - - - -
28 0.172 0.115: - - - - - -
                 

Comments:

No. 1. A rare case when the amplitude of the first overtone mode is much lower than that of the fundamental mode.

No. 6. The variability of GSC 5512-01099 was discovered by Siarhey Hadon, project VS-COMPAS (2012), from ROTSE-I/NSVS data (NSVS 15876164). Combined brightness of several stars was measured in the NSVS, the corresponding amplitudes are somewhat too low. The ROTSE data with photometric correction flags (usually rejected) were kept for the analysis. Asterisks in Table 4 mark the semi-amplitudes in the NSVS photometric system.

No. 16. Two systems of light elements were derived. The light elements for the CSS data are given in Table 3. The light elements for the Linear data are:

JD(max) = 2453600.273 + 0.421227 (the first-overtone period);

JD(max) = 2453600.363 + 0.564883 (the fundamental mode period).

No. 19. Two systems of light elements. The light elements for the CSS data are given in Table 3. The light elements for the Linear data are:

JD(max) = 2453600.125 + 0.413947 (the first-overtone period);

JD(max) = 2453600.225 + 0.554846 (the fundamental mode period).

No. 20. Two systems of light elements. The light elements for the CSS data are given in Table 3. The light elements for the Linear data are:

JD(max) = 2453600.300 + 0.444207 (the first-overtone period);

JD(max) = 2453600.065 + 0.596291 (the fundamental mode period).

No. 26. The variability of USNO-B1.0 0667-0901820 was discovered by Luyten (1938), who did not provide accurate coordinates. In the NSV catalog (Samus et al. 2007-2012), the star is numbered NSV 12483, the catalog position of NSV 12483 marked with a crosshair in our finding chart. Its type or period are not contained in the NSV catalog. The variability of USNO-B1.0 0667-0901820 was also reported by Keller et al. (2008; Id. 109453.71).The International Variable Star Index (VSX, AAVSO), based on Catalina survey data, gives the type RRC: (a possible RRC star) for the variable; initially, two periods were given, 0.201067 days and 0.290046 days. Later, in 2014, S. Otero gave it the period days, with the following remark: "It might be a double-mode pulsator (RRD) with a possible secondary period of 0.45397 d. (period ratio 0.7415) but more data are needed". I confirm the double-mode nature of this RR Lyrae variable, based on SWASP data. Combined brightness of two stars, USNO-B1.0 0667-0901820=var and the brighter neighbor GSC 6891-00928, was measured in the SWASP data, so the corresponding amplitudes are considerably underestimated. When plotting the phased light curves for the identified frequencies, and , I also subtracted variations of the mean brightness in the 1SWASP data, probably of instrumental origin. I considered the JD2453860-2454388 time range in the 1SWASP data. According to SSS data, it is USNO-B1.0 0667-0901820 that varies, and GSC 6891-00928 is a constant star. I was not able to reliably detect the double-mode behavior in the SSS data. Table 4 gives the combined-brightness semi-amplitudes in the SWASP photometric system. The SuperWASP observations are available as FITS tables, which were converted into ASCII tables using the OMC2ASCII program as described by Sokolovsky (2007).


Acknowledgments: Thanks are due to Dr. K.V. Sokolovsky for his advice concerning data retrieving. The author wishes to thank Dr. V.P. Goranskij for providing his software. This study was supported by the Russian Foundation for Basic Research (grant 13- 02-00664) and by the Programme "Non-stationary Phenomena of Objects in the Universe" of the Presidium of Russian Academy of Sciences.

References:

Antipin, S. V., Khruslov, A. V., 2013, Perem. Zvezdy Prilozh., 13, 15

Butters, O.W., West, R.G., Anderson, D.R., et al., 2010, Astron. and Astrophys., 520, L10

Drake, A.J., Djorgovski, S.G., Mahabal, A., et al., 2009, Astrophys. J., 696, 870

Drake, A. J., Catelan, M., Djorgovski, S. G., et al., 2013, Astrophys. J., 763, 32

Drake, A. J., Graham, M. J., Djorgovski, S. G., et al., 2014, Astrophys. J. Suppl., 213, 9

Huemmerich, S., Khruslov, A. V., 2014, Perem. Zvezdy Prilozh., 14, 2

Keller, S.C., Murphy, S., Prior, S., et al., 2008, Astrophys. J., 678, 851

Khruslov, A. V., 2007, Perem. Zvezdy Prilozh., 7, 7

Khruslov, A. V., 2010, Perem. Zvezdy Prilozh., 10, 11

Khruslov, A. V., 2011, Perem. Zvezdy Prilozh., 11, 25

Khruslov, A. V., 2012a, Perem. Zvezdy Prilozh., 12, 9

Khruslov, A. V., 2012b, Perem. Zvezdy Prilozh., 12, 25

Khruslov, A. V., Huemmerich, S., Bernhard, K., 2013, Perem. Zvezdy Prilozh., 13, 11

Lasker, B., Lattanzi, M.G., McLean, B.G., et al., 2008, Astron. J., 136, 735

Luyten, W.J., 1938, Publ. Astr. Obs. University Minnesota, 2, No.6, 114

Palaversa, L., Ivezic, Z., Eyer, L., et al., 2013, Astron. Journal, 146, 101

Poleski, R., 2014, PASP, 126, 509

Samus, N.N., Durlevich, O.V., Kazarovets, E.V., et al., 2007 - 2012, General Catalogue of Variable Stars, Centre de Donnees Astronomiques de Strasbourg, B/gcvs

Sesar, B., Stuart, J.S., Ivezic, Z., et al., 2011, Astron. J., 142, 190

Skrutskie, M.F., Cutri, R.M., Stiening, R., et al., 2006, Astron. J., 131, 1163

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Soszynski, I., Dziembowski, W. A., Udalski, A., et al., 2011, Acta Astronomica, 61, 1

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