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:
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FileName Lrecl Records Explanations
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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
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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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)
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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)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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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)
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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)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 22-Nov-2022