J/A+A/707/A58 Properties of variable mean mag OGLE RR Lyrae (Hajdu+, 2026)
RR Lyrae stars with variable mean magnitudes
Hajdu G., Jurcsik J., Catelan M., Pietrzynski G., Hocde V., Soszynski I.,
Udalski A., Lee C.-U., Kim D.-J.
<Astron. Astrophys. 707, A58 (2026)>
=2026A&A...707A..58H 2026A&A...707A..58H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry ; Optical
Keywords: circumstellar matter - stars: variables: RR Lyrae - dust, extinction -
Galaxy: bulge
Abstract:
A number of RR Lyrae stars show variable mean magnitudes in the OGLE
survey light curves of the Galactic bulge. Hitherto this phenomenon
was not studied, as it was generally assumed to be related to problems
with the photometry.
We investigate whether the mean magnitude variability of RR Lyrae
variables is due to genuine astrophysical phenomena.
We make use of the extended, and in many cases overlapping, light
curves from multiple microlensing surveys, to study RR Lyrae stars
with apparent mean-magnitude variations. A modified Fourier-series
based fitting method is introduced to analyze the light curves showing
mean-magnitude variations. Data from infrared surveys are also used to
construct spectral energy distributions (SEDs).
72 stars are presented where the mean-magnitude variations are most
probably of genuine astrophysical origin, and not the result of
problems with the photometry. The ratio of variation between the V and
I bands is compatible with variable extinction by dust in most cases,
but no infrared excess is detected in the SEDs. The occurrence rate of
the phenomenon, after correcting for selection effects, is ∼0.9%
among RR Lyrae variables in the OGLE bulge fields.
Description:
Due to the importance of RRL variables as stellar population tracers
and standard candles for distance determination, it is crucial to
investigate possible sources of bias affecting their properties.
Therefore, we have decided to perform a systematic revision of
mean-magnitude changes in the same sample of stars using photometry
from OGLE, as well as other surveys.
The main analysis was performed using the Johnson-Kron-Cousins V and
I-band time series photometric measurements of OGLE's Galactic bulge
RRL sample Soszynski et al. (2014AcA....64..177S 2014AcA....64..177S, Cat. J/AcA/64/177),
obtained during the survey's fourth phase (OGLE-IV). The currently
public data were extended for the analyzed objects with unpublished
data from the 2018 and 2019 observing seasons. Furthermore, we also
extracted from the OGLE internal catalogs the light curves of stars
within 10 arcseconds of RRL stars on our short list of candidates, and
used those to assess possible photometric contaminations. Light curves
available from the Massive Compact Halo Object (MACHO), Experience
pour la Recherche d'Objets Sombres phase 2 (EROS-2), Korea
Microlensing Telescope Network (KMTNet), Microlensing Observations in
Astrophysics (MOA) surveys, and the third phase of the OGLE project
(OGLE-III) were also revised during the analysis, in order to search
for independent evidence of mean-magnitude changes similar to those
detected in the OGLE-IV photometry.
During our initial search for mean-magnitude changes in RRL stars, we
have visually inspected the OGLE-IV light curves from the 2010-2017
observing seasons for the same sample of RRL stars as in our search
for binary RRL (2021ApJ...915...50H 2021ApJ...915...50H). A total of ∼250 stars were
selected for this long list of candidates, only omitting stars where
it was obvious from the light curves that the mean-magnitude changes
were caused by photometric problems. We applied criteria discussed in
section 'Search for RRL variables with changing mean-magnitudes'
leading us to a final sample of 72 RRL stars which all display
variable mean magnitudes in both their I- and V-band photometry. The
properties of these variables are summarized in table1.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 72 Property results of analysis for RR Lyrae with
detected mean-magnitude changes final sample
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See also:
J/AcA/64/177 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2014)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
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 OGLE ID of RR Lyrae star (Star)
22- 31 F10.8 d P Pulsation period adopted for the analysis
(Period)
33 A1 --- Cor Type of phase correction applied to data (OmC)
(1)
35 I1 --- Nbps Adopted number of breakpoints per season (Nbps)
37- 41 I5 --- NIband Number of data points in the I band (NI)
43- 44 I2 --- NIr Number of removed I band data points (NI_r)
46- 48 I3 --- NVband Number of data points in the V band (NV)
50 I1 --- NVr Number of removed V band data points (NV_r)
52- 56 F5.3 mag Amp Amplitude of mean-magnitude changes (dIDR)
58- 62 F5.3 --- rIV Amplitude ratio of the mean-magnitude changes
between the I and V bands (rIV)
64- 68 F5.3 --- e_rIV Uncertainty in rIV (e_rIV)
70 A1 --- u_rIV [*] Flag for uncertain rIV values (n_rIV)
72- 73 I2 --- NFI Number of harmonics adopted for the Fourier
series in the I band (FI)
75- 76 I2 --- NFV Number of harmonics adopted for the Fourier
series in the V band (FV)
78- 82 F5.1 --- dAIC Akaike Information Criterion difference in the
V band between the mean-magnitude changing and
simple Fourier series models (dAIC) (2)
84 I1 --- LC Long-term light-curve behavior (LC) (3)
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Note (1): Type of phase correction are as follows:
C = Constant period, no correction applied, 48 sources in our sample
P = Parabola subtracted, 19 sources in our sample
B = Binary solution subtracted, 5 sources in our sample
Note (2): As exposed in section 'Search for RRL variables with changing
mean-magnitudes', we calculate the difference in the Akaike
Information Criterion (AIC; Akaike 1974ITAC...19..716A 1974ITAC...19..716A) between the
traditional Fourier series and the mean-magnitude-changing Fourier
series solutions in the V band.
Note (3): Light-curve behaviors are as follows:
1 = Mostly monotonic increase or decrease, 41 sources in our sample
2 = Intervals of alternating increasing and decreasing periods,
10 sources in our sample
3 = Quasi-periodic variations, 15 sources in our sample
4 = Complex variations, 6 sources in our sample
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Acknowledgements:
Hajdu Gergely, ghajdu(at)camk.edu.pl
(End) Luc Trabelsi [CDS] 18-Dec-2025