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Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion

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Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion Research in Astron. Astrophys. 2011 Vol . 11 No. 8, 947–964 Research in http://www.raa-journal.org http://www.iop.org/journals/raa Astronomy and Astrophysics Photometric observations of three high mass X-ray binaries and a search for variations induced by orbital motion Gordon E. Sarty1, Bogumil Pilecki2,3, Daniel E. Reichart4,KevinM.Ivarsen4, Joshua B. Haislip4, Melissa C. Nysewander4, Aaron P. LaCluyze4, Helen M. Johnston5, Robert R. Shobbrook5,L´aszl´oL.Kiss6 andKinwahWu5,7 1 Departments of Psychology and Physics, University of Saskatchewan, 9 Campus Drive, Saskatoon, Saskatchewan S7N 5A5, Canada; [email protected] 2 Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland 3 Universidad de Concepcion, Departamento de Astronom¨ıa, Casilla 160-C, Concepcion, Chile 4 Department of Physics and Astronomy, University of North Carolina – Chapel Hill, CB 3255, Phillips Hall, Chapel Hill, NC 27599-3255, USA 5 School of Physics A28, University of Sydney, New South Wales 2006, Australia 6 Konkoly Observatory, H-1525 Budapest, P.O. Box 67, Hungary 7 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, United Kingdom Received 2011 April 20; accepted 2011 May 9 Abstract We searched for long period variation in V -band, IC-band and RXTE X-ray light curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5−5647, HD 110432 / 1H 1249−637 and HD 161103 / RX J1744.7−2713 in an attempt to discover orbitally induced variation. Data were obtained primarily from the ASAS database and were supplemented by shorter term observations made with the 24- and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier peri- odograms suggested the existence of long period variation in the V -band light curves of all three HMXBs, however folding the data at those periods did not reveal con- vincing periodic variation. At this point we cannot rule out the existence of long term V -band variation for these three sources and hints of longer term variation may be seen in the higher precision PROMPT data. Long term V -band observations, on the order of several years, taken at a frequency of at least once per week and with a pre- cision of 0.01 mag, therefore still have a chance of revealing long term variation in these three HMXBs. Key words: accretion — stars: Be stars — stars: neutron stars — stars: individual: LS 1698, HD 110432, HD 161103 — X-rays: binaries 1 INTRODUCTION High Mass X-ray Binaries (HMXBs) consist of a massive star orbited by a compact object like a neutron star, a black hole or, as is proposed for γ Cas analogs, a white dwarf. A major class of HMXBs, the BeXs, have a Be star as the primary massive star. The orbital periods of many BeXs are 948 G. E. Sarty et al. known from their periodic Type I X-ray outbursts. Such outbursts are believed to be caused by the passage of a neutron star through the Be star’s equatorial decretion disk when increased accretion onto the neutron star occurs (Okazaki & Negueruela 2001). These Type I X-ray outbursts can also be accompanied by optical outbursts which can confirm the orbital period (Coe & Edge 2004). However, many BeXs, including the three of interest here, are persistent X-ray sources, indicating a more uniform accretion rate and circular orbits with longer periods. The lack of regular X-ray outbursts means that the orbital periods for many of the persistent BeXs are unknown. In spite of the expected lack of corresponding optical outbursts, optical searches for orbital periodicity can be successful (Coe et al. 2005; Schmidtke & Cowley 2006). Here we report on the search for long periods in the optical photometry of three persistent BeXs: LS 1698, the optical counterpart to RX J1037.5−5647; HD 110432, the optical counterpart to 1H 1249−637; and HD 161103, the optical counterpart to RX J1744.7−2713. The source LS 1698 has been argued to be an analog of X Per (Reig & Roche 1999) while HD 110432 and HD 161103 have been argued to be analogs of γ Cas. X Per is a BeX with a neutron star and a long orbital period of 250.3 d (Delgado-Mart´ı et al. 2001). The star γ Cas has been proposed to contain a white dwarf as its compact object, although single star models for γ Cas exist (Lopes de Oliveira et al. 2006, 2007). The main component of our data came from the All Sky Automated Survey (ASAS, Pojmanski (1997)) supplemented with confirming data obtained with the 24 and 40 inch telescopes of the Australian National University (ANU) and with one of the 16 inch telescopes of the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT, Reichart et al. 2005) array. This paper is organized as follows. In Section 2 we present the photometric observations, in- cluding RXTE X-ray photometry for LS 1698. Section 3 gives the results of formal searches for periods in the data using Fourier techniques. In Section 4 we give a brief review of what is currently known about the three HMXBs to motivate further investigation of these sources. Our conclusions are summarized in Section 5. 2 OBSERVATIONS A total of four small telescopes/telescope systems were used to make optical observations of LS 1698, HD 110432 and HD 161103. The observation log is given in Table 1. The bulk of the data were obtained with the ASAS-3 telescope system. ASAS-3 consists of two wide field 87-mm diameter f2.8 Minolta telephoto lenses, one equipped with a Johnson V filter, the other with a Johnson-Cousins IC filter. The individual telescopes use Apogee AP-10 2048×2048 pixel CCD cameras as detectors. ASAS-3 is an automated instrument and produces reduced photom- etry automatically. As part of the reduction process, the software rates the quality of the data. Only Table 1 Observation Log Source Date Filter Telescope d/mon/yr LS 1698 21/12/2000 to 3/12/2009 V ,IC ASAS 24/8/2005 to 5/9/2005 B,V ,R,IC ANU 40-in 24/3/2006 to 1/4/2006 B, V , R, IC ANU 24-in 17/7/2007 to 28/7/2007 B, V , R, IC ANU 40-in 8/12/2008 to 12/2/2009 V , IC PROMPT-5 HD 110432 29/11/2000 to 29/7/2009 V , IC ASAS HD 161103 31/1/2001 to 2/7/2009 V , IC ASAS 4/8/2002 to 14/10/2002 B, V , IC ANU 24-in 29/8/2005 to 5/9/2005 B, V , R, IC ANU 40-in 23/3/2006 to 1/4/2006 B, V , R, IC ANU 24-in 19/7/2006 to 19/7/2006 B, V , R, IC ANU 40-in Three Long Period X-ray Binaries 949 N i h a E e f b d g c Comparison / Check stars Star RA Dec BV RIC a 10 37 33.4 –56 47 19.4 12.82 12.45 12.12 11.71 c 10 37 47.17 –56 51 29.2 11.62 11.17 10.81 10.41 d 10 37 23.9 –56 51 11.4 12.52 12.05 11.67 11.28 e 10 36 52.05 –56 48 20.9 11.54 11.18 10.83 10.41 Fig. 1 Comparison/check stars in the field of LS 1698 as determined from data obtained with the ANU 24- and 40-in telescopes at Siding Spring Observatory. Errors are on the order of 0.01 to 0.05 mag. The target star is marked with two lines in the center. Positions and magnitudes are listed for those stars whose magnitudes and colors make them the most useful for differential photometry with the target. North is up, east to the left. observations rated as ‘grade A’ were used. The ASAS instrument is located at the Las Campanas Observatory in Chile. Two telescopes owned by the ANU and located at the Siding Spring Observatory in Australia were used. These telescopes had apertures of 24 and 40 inches. For the first observing run with the ANU 24-in telescope, from 4/8/2002 to 14/10/2002, for HD 161103 a pulse-counting GaAs photo-multiplier tube photometer was used with a filter wheel controlled by a computer that also recorded photon counts in the B, V and IC bands (Bessell 1990). Transformations to the standard Cape UBVRI system were made on one night from 15 stars in the Regions E5, E7 and E9, using the values of Menzies et al. (1989). On each night, the V , (B − V ) and (V − I) magnitudes of LS 1698 were referred to as the two standards E6/04 and E6/66, which are approximately 18◦ from the source. The internal photometric errors of the observations were of the order 0.002 to 0.004 mag. Referral to the fairly distant E6 Region stars adds an uncertainty of a similar amount on average, depending on the air-mass and the quality of the night, due to uncertainty in the differential extinction corrections. The final differential photometric errors were therefore in the range 0.005 to 0.007 mag. 950 G. E. Sarty et al. N g i n o f e c p E l a b d k h j m Comparison / Check stars Star RA Dec BV RIC a 17 44 41.9 –27 14 31.5 12.881 12.082 11.587 11.053 b 17 44 44.0 –27 14 22.5 13.056 12.590 12.311 12.002 d 17 44 52.1 –27 16 10.5 11.298 10.731 10.427 10.081 f 17 44 12.9 –27 11 11.5 12.525 11.936 11.602 11.228 j 17 44 28.4 –27 18 57.4 12.849 12.222 11.833 11.392 k 17 44 40.2 –27 17 33.7 13.281 12.648 12.216 11.817 l 17 44 47.3 –27 14 05.5 13.265 12.716 12.352 11.983 Fig.
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