J/A+A/575/L6 Optical observations of LS I +61 303 (Paredes-Fortuny+, 2015)
Evidence of coupling between the thermal and nonthermal emission in the
gamma-ray binary LS I +61 303.
Paredes-Fortuny X., Ribo M., Bosch-Ramon V., Casares J., Fors O., Nunez J.
<Astron. Astrophys. 575, L6 (2015)>
=2015A&A...575L...6P 2015A&A...575L...6P
ADC_Keywords: Binaries, X-ray ; Stars, Be ; Photometry, CCD ; Equivalent widths
Keywords: X-rays: binaries - X-rays: individual: LS I +61 303 -
binaries: close - stars: emission-line, Be - gamma rays: stars
Abstract:
The gamma-ray binary LS I +61 303 is composed of a Be star and a
compact companion orbiting in an eccentric orbit. Variable flux
modulated with the orbital period of ∼26.5d has been detected from
radio to very high-energy gamma-rays. In addition, the system presents
a superorbital variability of the phase and amplitude of the radio
outbursts with a period of ∼4.6yr. We present optical photometric
observations of LS I +61 303 spanning ∼1.5yr (table 1) and
contemporaneous H-alpha equivalent width (EW) data (table 2).
The optical photometry shows, for the first time, that the known
orbital modulation suffers a positive orbital phase shift and an
increase in flux for data obtained 1-yr apart. The orbital modulation
of the EW presents, for the first time, a positive orbital phase
shift. These orbital phase shifts of the thermal indicators are in
line with the observed behavior for nonthermal indicators, such as
X-ray or radio emission. This shows that there is a strong coupling
between the thermal and nonthermal emission processes in the gamma-ray
binary LS I +61 303.
Description:
In Table 1 we present the already reduced differential optical
photometry of the gamma-ray binary LS I +61 303 obtained with the
robotic Telescope Fabra-ROA Montsec (TFRM; 0.5m aperture, 0.78m
primary mirror) at the Observatori Astronomic del Montsec (Lleida,
Spain; see Fors et al. 2013PASP..125..522F 2013PASP..125..522F). The observations span
from 2012 July 31 to 2014 March 7 with 71 nights of good data. The
target was observed around 20 times per night with exposures of 5-10s.
The passband filter is SCHOTT GG475 (lambda>475nm).
We conducted the data reduction and analysis using a pipeline
developed in Python following these steps: standard calibration of the
images using IRAF (implemented through PyRAF), aperture photometry
using the PHOT package from IRAF (PyRAF) with an aperture radius of
7.5-pixels, and correction of the lightcurves using a weighted average
differential magnitude correction method based on Broeg et al.
(2005AN....326..134B 2005AN....326..134B). The lightcurve of LS I +61 303 has been
corrected using 145 weighted reference stars up to 4mag fainter than
the target and as close as possible to it (<0.25deg). Finally, we
averaged the corrected magnitudes of the target on a nightly basis,
and we used and artificial offset to a mean magnitude of 10.7mag. The
nightly photometric uncertainties are estimated as the standard
deviation of the magnitudes of the target obtained from the individual
images for each night.
In Table 2 we present the already reduced H-alpha equivalent width
(EW) data of LS I +61 303 obtained using FRODOspec on the robotic 2.0m
Liverpool telescope at the Observatorio del Roque de los Muchachos (La
Palma, Spain). The data span from 2012 July to 2014 January 15 with
104 measurements, with one 600s exposure per night.
The data have been obtained with the same setup, and reduced in the
same way as in Casares et al. (2012MNRAS.421.1103C 2012MNRAS.421.1103C). We assumed that
the uncertainties of the EW are at the 10% level. The adopted
convention is positive for emission.
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
02 40 31.67 +61 13 45.6 LS I +61 303 = V* V615 Cas
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 23 71 Differential optical photometry of LS I +61 303
table2.dat 23 104 H-α equivalent width of LS I +61 303
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See also:
J/ApJ/656/437 : LSI +61 303 radial velocities and Halpha EW (Grundstrom+, 2007)
J/ApJ/698/514 : Radial velocities of LSI+61 303 and LS 5039 (Aragona+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d MJD Modified Julian Day
12- 17 F6.3 mag mag Differential magnitude
19- 23 F5.3 mag e_mag rms uncertainty on mag
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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- 12 F12.4 d HJD Heliocentric Julian Day
14- 18 F5.2 0.1nm EW H-α equivalent width
20- 23 F4.2 0.1nm e_EW rms uncertainty on EW
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Acknowledgements:
Xavier Paredes-Fortuny, xparedes(at)am.ub.es
(End) X. Paredes-Fortuny [Univ. Barcelona], P. Vannier [CDS] 22-Jan-2015