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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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)
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.
Acknowledgements: Geza Kovacs, kovacs(at)szombat.konkoly.hu
(End) Patricia Vannier [CDS] 24-Jun-2009
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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