J/A+A/500/917 Variable stars in LMC MACHO fields 1 & 79 (Szulagyi+, 2009)
Application of the trend filtering algorithm to the MACHO database.
Szulagyi J., Kovacs G., Welch D.L.
<Astron. Astrophys. 500, 917 (2009)>
=2009A&A...500..917S 2009A&A...500..917S
ADC_Keywords: Stars, variable ; Magellanic Clouds ; Photometry
Keywords: methods: data analysis - stars: variables: general -
galaxies: Magellanic Clouds
Abstract:
Because of the strong effect of systematics/trends in variable star
observations, we apply the Trend Filtering Algorithm (TFA) to a subset
of the MACHO database and search for variable stars. TFA has been
applied successfully in planetary transit searches, where weak,
short-lasting periodic dimmings are sought in the presence of noise
and various systematics (due to, e.g., imperfect flat fielding,
crowding, etc). These latter effects introduce colored noise in the
photometric time series that can completely overwhelm the signal. By
using a large number of available photometric time series of a given
field, TFA utilizes the fact that the same types of systematics appear
in several/many time series of the same field. As a result, we attempt
to reproduce each target time series by a linear combination of
templates, optimized by least-squares. After a signal has been
identified in the residuals between the original time series and the
systematics computed by TFA, we reconstruct the signal by employing
the full model, including the signal, systematics and noise. We apply
TFA to the brightest ∼5300 objects from subsets of each of the MACHO
Large Magellanic Cloud fields #1 and #79. We find that the Fourier
frequency analysis performed on the original data detects some 60% of
the objects as trend-dominated. This figure decreases essentially to
zero after using TFA. In total, we detect 387 variables in the two
fields, 183 of which would have remained undetected without using TFA.
Where possible, we give preliminary classification of the variables
found.
Description:
Tables 1 and 2 give the brief summary of the variables found in the
course of the analysis. Main properties are listed and preliminary
classifications are given (this latter is ambiguous in some cases, as
indicated by question marks). Time series (original, published by the
MACHO project and TFA-filtered) can be accessed at:
http://www.konkoly.hu/staff/kovacs/macho_tfa/
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 58 166 Variable stars in the MACHO field #1
table2.dat 58 221 Variable stars in the MACHO field #79
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See also:
II/247 : Variable Stars in the Large Magellanic Clouds (MACHO, 2001)
J/A+A/313/841 : MACHO LMC No.1 microlensing event (Dominik+, 1996)
J/AJ/114/326 : MACHO Variables V. (Alcock+ 1997)
J/ApJ/542/257 : MACHO LMC first-overtone RR Lyrae (Alcock+, 2000)
J/AJ/127/334 : MACHO LMC first-overtone RR Lyrae variables (Alcock+, 2004)
J/ApJ/562/337 : High proper-motion stars from MACHO astrometry (Alcock+, 2001)
J/AJ/124/2039 : LMC blue variable stars from MACHO (Keller+, 2002)
J/ApJ/598/597 : Frequency analysis of fundamental-mode RR Lyrae (Alcock+ 2003)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Name Name, HHMMSSss+DDMMSSs
18- 23 F6.3 mag Vmag Average Johnson V magnitude
25- 30 F6.3 mag V-Rc Average Johnson V minus Cousins R color
32- 40 F9.6 d-1 Freq Frequency (1/P, where P is the dominant
period) (1)
42- 45 F4.1 --- SNR Signal-to-noise ratio (2)
49- 55 A7 --- VType Variable type (4)
58 I1 --- TFA [0/1] Discovery type (3)
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Note (1): The frequencies for type EB variables are given with larger
number of digits, because of the higher sensitivity of the eclipse
shape to the precision of the orbital period.
Note (2): The definition of the signal-to-noise ratio (SNR) is described
in the paper.
Note (3): Discovery type is numbered:
1 = TFA (Trend Filtering Algorithm) detection
0 = pre-TFA detection
Note (4): the classification of the variable is preliminary and
approximate. The following classes are defined:
LPV = not eclipsing and period longer than ∼10days
and brighter than the HB level of V≃19mag
FU Cep = fundamental mode Cepheid.
FO Cep = first overtone mode Cepheid.
SO Cep = second overtone mode Cepheid.
RRab = fundamental mode RR Lyrae.
RRc = first overtone mode RR∼Lyrae.
EB = eclipsing binaries of any type.
B = B-type pulsators, V≲18.0, V-R≲0.1
d Sct = δ Sct, frequency is greater than 5d-1 and 0≤V-R≤ 0.3
Hump = hump/eruption in the light curve.
Misc = anything that cannot be classified.
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Acknowledgements:
Geza Kovacs, kovacs(at)szombat.konkoly.hu
(End) Patricia Vannier [CDS] 24-Jun-2009