J/MNRAS/487/5584     First-overtone RR Lyrae stars from OGLE     (Netzel+, 2019)

The census of non-radial pulsation in first-overtone RR Lyrae stars of the OGLE Galactic bulge collection. Netzel H., Smolec R. <Mon. Not. R. Astron. Soc., 487, 5584-5592 (2019)> =2019MNRAS.487.5584N 2019MNRAS.487.5584N (SIMBAD/NED BibCode)
ADC_Keywords: Stars, horizontal branch ; Stars, variable ; Milky Way ; Optical Keywords: stars: horizontal branch - stars: oscillations - stars: variables: RR Lyrae Abstract: We analysed photometry for the up-to-date collection of the first-overtone RR Lyrae stars (RRc; 11415 stars) and double-mode RR Lyrae stars (RRd; 148 stars) towards the Galactic bulge from the Optical Gravitational Lensing Experiment (OGLE). We analysed frequency spectra of these stars in search for additional, low-amplitude signals, beyond the radial modes. We focused on stars from two groups: RR0.61 and RR0.68. In the first group, additional low-amplitude signals have periods shorter than the first-overtone period; period ratios fall in the 0.60-0.64 range. In the second group, additional low-amplitude signals have periods longer than the first-overtone period; period ratios tightly cluster around 0.68. Altogether we have detected 960 and 147 RR Lyrae stars that belong to RR0.61 and RR0.68 groups, respectively, which yield the incidence rates of 8.3 and 1.3 per cent of the considered sample. We discuss statistical properties of RR Lyrae stars with additional periodicities. For RR0.61 group we provide strong arguments that additional periodicities are connected to non-radial pulsation modes of degrees l=8 and l=9, as proposed by Dziembowski. We have also detected two double-periodic variables, with two close periodicities, similar to RR Lyrae variable V37 in NGC 6362. Properties of these peculiar variables, which may form a new group of double-mode pulsators, are discussed. Description: The data used for analysis were gathered during the fourth phase of the OGLE project, which started in 2010 and is ongoing (Udalski et al. 2015AcA....65....1U 2015AcA....65....1U). Eight seasons of observations carried out in 2010-2017 in the Galactic bulge are available for the analysis. We used observations in the I filter only, as these are more numerous than in the V filter. The input sample for the analysis comprises 11415 RRc stars. Because of the numerous samples, the study was largely automatic. We have detected 960 RR0.61 stars, i.e. stars with additional, low-amplitude variability and period ratios, Px/P1O, in the 0.6-0.64 range (see Table 1). The incidence rate of this phenomenon, considering the whole OGLE sample, is thus 8.3 per cent. The real incidence rate is much higher however. Our previous analysis of selected OGLE-IV fields with the highest observing cadence and hence of relatively low-noise points towards incidence rate of 27 per cent (Netzel et al. 2015MNRAS.453.2022N 2015MNRAS.453.2022N, Cat. J/MNRAS/453/2022). Space photometry, on the other hand, indicates that RR0.61 must be common, as nearly all RRc/RRd stars observed from space belong to RR0.61 class (Molnar et al. 2015MNRAS.452.4283M 2015MNRAS.452.4283M, Cat. J/MNRAS/452/4283; Moskalik et al. 2015MNRAS.447.2348M 2015MNRAS.447.2348M). We have detected 147 RR0.68 stars, i.e. stars with the additional low-amplitude variability and period ratios P1O/Px close to 0.686 (see Table 2). The incidence rate is thus 1.3 per cent. 128 stars are new detections. We note that we still lack the interpretation for this mysterious group in which additional signal has period longer that the period of the radial fundamental mode (not detected in these stars). File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 108 1127 Sample table with properties of RR0.61 stars table2.dat 98 147 Sample table with properties of RR0.68 stars -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 20 A20 --- Name Star name (OGLE-BLG-RRLYR-NNNNN) 22- 32 F11.9 d P1O First overtone period 34- 44 F11.9 d e_P1O Error on P1O 46- 55 F10.8 d Px Period of the additional signal 57- 66 F10.8 d e_Px Error on Px 68- 74 F7.5 --- Px/P1O Ratio between the two periods 76- 82 F7.5 mag A1O Amplitude of the first overtone 84- 90 F7.5 mag e_A1O Error on A1O 92- 96 F5.3 --- Ax/A1O Ratio of amplitude of the additional signal to the amplitude of the first-overtone mode 98-108 A11 --- Remarks Remarks (1) -------------------------------------------------------------------------------- Note (1): Remarks as follows: bl = Blazhko effect is present in the star (19/949) cand. = additional signal is weak (around S/N=4) or its daily aliases are higher (130/949) 0.5fx = subharmonic of the additional signal is detected (114/949) RRd = double-mode RR Lyrae star (11/949) -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 20 A20 --- Name Star name (OGLE-BLG-RRLYR-NNNNN) 22- 31 F10.8 d P1O First overtone period 33- 42 F10.8 d e_P1O Error on P1O 44- 52 F9.7 d Px Period of the additional signal 54- 62 F9.7 d e_Px Error on Px 64- 70 F7.5 --- Px/P1O Ratio between the two periods 72- 78 F7.5 mag A1O Amplitude of the first overtone 80- 86 F7.5 mag e_A1O Error on A1O 88- 92 F5.3 --- Ax/A1O Ratio of amplitude of the additional signal to the amplitude of the first-overtone mode 94- 98 A5 --- Remarks Remarks (1) -------------------------------------------------------------------------------- Note (1): Remarks as follows: bl = Blazhko effect is present in the star (24/147) comb. = there is a combination between the first overtone and the additional signal (18/147) -------------------------------------------------------------------------------- History: From electronic version of the journal
(End) Ana Fiallos [CDS] 22-Nov-2022
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