J/AJ/169/310 Characteristics of Blazhko stars from ZTF & LINEAR (Donev+, 2025)
Search for the Blazhko effect in field RR Lyrae stars using LINEAR and ZTF light
curves.
Donev E., Ivezic Z.
<Astron. J., 169, 310 (2025)>
=2025AJ....169..310D 2025AJ....169..310D
ADC_Keywords: Stars, variable; Photometry; Optical
Keywords: RR Lyrae variable stars
Abstract:
We analyzed the incidence and properties of RR Lyrae stars that show
evidence for amplitude and phase modulation (the so-called Blazhko
Effect) in a sample of ∼3000 stars with LINEAR and ZTF light
curve data collected during the periods of 2002-2008 and 2018-2023,
respectively. A preliminary subsample of about ∼500 stars was
algorithmically preselected using various data quality and light curve
statistics, and then 228 stars were confirmed visually as displaying
the Blazhko effect. This sample increases the number of field RR Lyrae
stars displaying the Blazhko effect by more than 50% and places a
lower limit of (11.4±0.8)% for their incidence rate. We find
that ab type RR Lyrae that show the Blazhko effect have about 5%
(0.030 day) shorter periods than starting sample, a 7.1σ
statistically significant difference. We find no significant
differences in their light curve amplitudes and apparent magnitude
(essentially, signal-to-noise ratio) distributions. No period or other
differences are found for c type RR Lyrae. We find convincing examples
of stars where the Blazhko effect can appear and disappear on
timescales of several years. With time-resolved photometry expected
from the Legacy Survey of Space and Time, a similar analysis will be
performed for even larger samples of field RR Lyrae stars in the
southern sky and we anticipate a higher fraction of discovered Blazhko
stars due to better sampling and superior photometric quality.
Description:
For our starting sample, we used ∼3000 field RR Lyrae stars with
light curves obtained by the Lincoln Near-Earth Asteroid Research
(LINEAR) survey. In order to study long-term changes in light curves,
we also utilized light curves obtained by the Zwicky Transient Factory
(ZTF) survey, which monitored the sky ∼15 yr after LINEAR.
The sample used in this work contains 2196 ab-type and 745 c-type RR
Lyrae, selected using classification labels and the gi color index
from Palaversa+2013 (J/AJ/146/101).
LINEAR uses two 1m optical telescopes at the Lincoln Laboratory
Experimental Test Site (ETS) near Socorro, New Mexico, USA. The survey
covered about 10,000 deg2 of the northern sky in white light (no
filters were used). Light curves used in this work include, on
average, 270 data points collected between 2002 December and 2008
September.
The ZTF is an optical time-domain survey that uses the Palomar 48-inch
Schmidt telescope in San Diego, California, and a camera with 47deg2
field of view. The data set analyzed here was obtained with SDSS-like
g, r, and i band filters. Light curves for objects in common with the
LINEAR RR Lyrae sample typically have smaller random photometric
errors than LINEAR light curves because ZTF data are deeper. ZTF data
used in this work were collected between 2018 February and 2023
December, on average about 15 yr after obtaining LINEAR data. The
median number of observations per star for ZTF light curves is ∼500.
The resulting sample consisted of 2857 RR Lyrae stars with both LINEAR
and ZTF data. The fractions of RRab and RRc type RR Lyrae in this
sample, 71% RRab and 29% RRc type, are consistent with results from
other surveys (e.g., Sesar+2010, J/ApJ/708/717;
Clementini+2023, J/A+A/674/A18).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 111 228 Confirmed Blazhko stars
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJ/598/597 : Frequency analysis of fundamental-mode RR Lyrae (Alcock+, 2003)
J/MNRAS/377/1263 : Multiperiodic RR Lyrae in ASAS catalog (Szczygiel+, 2007)
J/AcA/59/1 : VI light curves of LMC RR Lyrae stars (Soszynski+, 2009)
J/A+A/520/A108 : CoRoT 101128793 light curves (Poretti+, 2010)
J/ApJ/708/717 : Light curve templates of RR Lyrae stars (Sesar+, 2010)
J/AcA/60/165 : VI light curves of SMC RR Lyrae (Soszynski+, 2010)
J/AcA/61/1 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2011)
J/MNRAS/411/1744 : Observations of RR Lyr stars in M5 (Szeidl+, 2011)
J/AJ/146/101 : LINEAR. III. Catalog of periodic variables (Palaversa+, 2013)
J/AJ/146/21 : LINEAR. II. Catalog of RR Lyrae stars (Sesar+, 2013)
J/A+A/549/A101 : Known Galactic field Blazhko stars (Skarka, 2013)
J/ApJS/213/31 : Blazhko effect from 4yr of Kepler data (Benko+, 2014)
J/A+A/570/A100 : BVRc light curves of 5 CoRoT RR Lyrae stars (Szabo+, 2014)
J/MNRAS/466/2602 : Blazhko effect in Galactic RR Lyrae (Prudil+, 2017)
J/MNRAS/480/1229 : Blazhko effect in the 1st overtone RR Lyrae (Netzel+, 2018)
J/MNRAS/494/1237 : Blazhko effect in Galactic RR Lyrae II (Skarka+, 2020)
J/A+A/674/A18 : Gaia DR3. The RR Lyrae sample (Clementini+, 2023)
J/A+A/678/A104 : M80 anomalous variable stars (Molnar+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- LINEAR [158779/24216004] LINEAR identifier
10- 17 F8.6 d Per-L [0.26/0.73] Computed light-curve period,
LINEAR
19- 26 F8.6 d Per-Z [0.26/0.73] Computed light-curve period, ZTF
28- 30 I3 --- N-L [150/638] Number of data points, LINEAR
32- 35 I4 --- N-Z [168/3881] Number of data points, ZTF
37- 39 F3.1 --- chi2r-L [0.7/6.6] Robust χ2 per degree of
freedom, LINEAR
41- 44 F4.1 --- chi2r-Z [1.1/11.6] Robust χ2 per degree of
freedom, ZTF
46- 50 F5.1 --- chi2-L [0.5/121.4] Ordinary χ2 per degree of
freedom, LINEAR
52- 56 F5.1 --- chi2-Z [1.3/186.9] Ordinary χ2 per degree of
freedom, ZTF
58- 61 F4.2 mag Amp-L [0.26/1.24] Light-curve amplitude, LINEAR
63- 66 F4.2 mag Amp-Z [0.23/1.49] Light-curve amplitude, ZTF
68- 71 F4.2 mag dAmp [0/0.5] Difference, |Amp-L - Amp-Z|
73- 78 F6.4 --- Str-Bp-L [1.4/3.8] Strength, Blazhko peaks, LINEAR
80- 85 F6.4 --- Str-Bp-Z [1.37/3.84] Strength, Blazhko peaks, ZTF
87- 94 F8.4 d Per-Bp-L [6.6/357.8] Period of Blazhko peaks, LINEAR
96- 103 F8.4 d Per-Bp-Z [6.5/356.6] Period of Blazhko peaks, ZTF
105 I1 --- Type [1,2] Light-curve type (1)
107 A1 --- Flag Detection significance flag (2)
109 I1 --- B-s [0/9] Selection score, number of points
scored from the selection algorithm
(Section 3.1) (3)
111 I1 --- B-f [1/2] Selection score, Section 3.2 (4)
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Note (1): Light curve type as follows:
1 = ab (180 occurrences)
2 = c (48 occurrences)
Note (2): Detection significance flag as follows:
Z = The Zwicky Transient Factory (ZTF), an optical time-domain survey
that using the Palomar 48-inch Schmidt telescope in California, USA
(4 occurrences)
L = The Lincoln Near-Earth Asteroid Research project (LINEAR) using two
1m optical telescopes at the Lincoln Laboratory Experimental Test Site
(ETS) near Socorro, New Mexico, USA (10 occurrences)
- = No detection. Note that Str-Bp & Per-Bp are not reliable in these cases.
(214 occurrences)
Note (3): We used a simple scoring algorithm, optimized through trial and error,
that utilized the two values of χ2, augmented by period and amplitude
differences, as follows. A star could score a maximum of nine points, and a
minimum of five points was required for further visual analysis. The χ2
selection boundaries are illustrated in Figure 2. If either value of χ2
exceeded 5, or both exceeded 3, a star was awarded 5 points and immediately
selected for further analysis. If these χ2 criteria were not met, a
star could still be selected by meeting less stringent χ2 selection if
it also had large period or amplitude difference between LINEAR and ZTF data
sets. Stars with at least one value of χ2 above 2 would receive 3
points and those with at least one χ2 above 3 would receive 4 points.
A period difference exceeding 2e-4day would be awarded 1 and 2 points for
exceeding 5e-4day. Analogous limits for amplitude difference were 0.05mag
and 0.15mag, respectively.
Note (4): Score occurrences as follows:
1 = 214 occurrences
2 = 14 occurrences
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 09-Mar-2026