======================================================================== *TITLE_1! WR 22, investigation of the colliding winds around apastron ======================================================================== *OM_CONTACT! J.-M. Vreux *OM_CONTACT_EMAIL! Panoptix@astro.ulg.ac.be ======================================================================== *SCIENCE_OBJECTIVES! WR 22 is an eclipsing binary (Gosset et al, 1991) of spectral type WN7+abs + O in the Carina OB1 association. The photometric eclipse corresponds to the occultation of the secondary by the WR primary and its dense wind around the periastron passage. Recently, Rauw et al. (1996a) used an extensive set of high resolution spectra of WR 22 to investigate the orbit of this eccentric binary (e = 0.56 , P = 80.3 days). From the radial velocities of the secondary's absorption lines, Rauw et al. derive a minimum mass of the WN7+abs primary of 72 solar masses, making it the most massive star known so far in a binary system. This high mass together with a hydrogen mass-fraction of +/- 0.4 determined from the visible spectrum (Crowther et al., 1995a) suggest that WR 22 is at the very beginning of its Wolf-Rayet evolution and is probably still a core hydrogen burning object which has evolved from a progenitor of at least 90-110 solar masses (Rauw et al., 1996a). EINSTEIN observations of WR 22 obtained around the upper conjunction, i.e. near apastron when the O star is in front, indicate a bright X-ray source, whereas the system appears much fainter around the periastron passage, when the WR primary with its denser wind is in front (Pollock, 1987). These observations are in line with the picture of a colliding winds binary system where a copious X-ray emission is generated near the interface between the winds of the two stars. The X-ray modulation observed in the case of WR 22 results from the variable column density along the line of sight. Observations of this system with a better S/N ratio and a better phase coverage are the topic of another XMM-GT proposal. In the present proposal we suggest to complement these observations with two additional pointings of WR 22 at orbital phases close to apastron to investigate the impact of intrinsic variability on the X-ray light curve of this system. This proposal is part of a comprehensive program aimed at the study of stars in different evolutionary stages. ========================================================================== *TOTAL_NO_POINTINGS! 2 ;one, but 2 times, at different orbital phases. *TOTAL_TIME! 20 *PRIME_INSTRUMENT! EPIC SPECIAL! Time constrained observations ========================================================================== *TECHNICAL_INFO! There are four visibility windows for WR 22 over the first two years of XMM operations. Each window covers about 40 spacecraft orbits i.e. 80 days. During a visibility window, the duration of visibility is 145 ksec per orbit. The present proposal is a supplement to another, more extensive GT proposal on WR 22, hereafter called the main proposal. The first observation should be centered on the apastron passage of WR 22 i.e. Ti = H.J.D. 2451452.782 + n * 80.325 days and the second one about 6.7 +/- 2 days later. The observations in this proposal should not be done during the same binary orbital cycle than the observations requested in the main proposal, but they can be done during any other visibility window. The X-ray luminosity derived from EINSTEIN observations near apastron is 8e32 erg s-1. For a column density of 5e20 cm-2 and a distance of 2.6 kpc, we estimated the following count rates using the PIMMS software: 0.57 cts s-1 for EPIC and 0.041 cts s-1 for the RGS. Given the optical brightness of WR 22, the thick filter is required for the EPIC observations (TBC). We suggest to use the pn EPIC instrument in full frame imaging mode with a TBD value of w. For the EPIC MOS detectors the partial window imaging mode is probably required to avoid pile-up (TBC). Data are requested on the whole FOV in particular to study the possible diffuse background emission from the Carina nebula. =========================================================================== *TARGET_NAME_01! WR 22 TARGET_ALT_NAME_01! HD 92740 *TARGET_RA_01! 10 41 18 *TARGET_DEC_01! -59 40 37 *TARGET_EXPOSURE_01! 10 ;ksec (see technical information) *TARGET_PRIORITY_01! C TARGET_MODE_EPIC_MOS1_01! [Prime Partial Window]; partial window imaging (TBC) TARGET_MODE_EPIC_MOS2_01! [Prime Partial Window]; partial window imaging (TBC) TARGET_MODE_EPIC_PN_01! full field imaging (TBC) TARGET_FILTER_EPIC_MOS1_01! [Thick] TARGET_FILTER_EPIC_MOS2_01! [Thick] TARGET_FILTER_EPIC_PN_01! [Thick] TARGET_MODE_RGS1_01! TARGET_MODE_RGS2_01! TARGET_MODE_OM_01! ;U filter with obscuration bar or safety (TBD) TARGET_FILTER_OM_01! [Bar, Closed] ;U filter with obscuration bar or safety (TBD) TARGET_OBS_DATE_01! [constrained] TARGET_COMMENT_01! time constrained observations The first observation should be centered on the apastron passage of WR 22 i.e. Ti = H.J.D. 2451452.782 + n * 80.325 days and the second one some 6.7 +/- 2 days later. These observations should be carried out during another binary orbital cycle than those requested in the main proposal. Data are requested on the whole FOV in particular to study the possible diffuse background emission from the Carina nebula. =========================================================================== *TARGET_NAME_02! WR 22 TARGET_ALT_NAME_02! HD 92740 *TARGET_RA_02! 10 41 18 *TARGET_DEC_02! -59 40 37 *TARGET_EXPOSURE_02! 10 ;ksec (see technical information) *TARGET_PRIORITY_02! C TARGET_MODE_EPIC_MOS1_02! [Prime Partial Window] ;partial window imaging (TBC) TARGET_MODE_EPIC_MOS2_02! [Prime Partial Window] ;partial window imaging (TBC) TARGET_MODE_EPIC_PN_02! full field imaging (TBC) TARGET_FILTER_EPIC_MOS1_02! [Thick] TARGET_FILTER_EPIC_MOS2_02! [Thick] TARGET_FILTER_EPIC_PN_02! [Thick] TARGET_MODE_RGS1_02! TARGET_MODE_RGS2_02! TARGET_MODE_OM_02! ;U filter with obscuration bar or safety (TBD) TARGET_FILTER_OM_02! [Bar, Closed] ;U filter with obscuration bar or safety (TBD) TARGET_OBS_DATE_02! [constrained] TARGET_COMMENT_02! time constrained observations The first observation (01) should be centered on the apastron passage of WR 22 i.e. Ti = H.J.D. 2451452.782 + n * 80.325 days and the second one (02) some 6.7 +/- 2 days later. These observations should be carried out during another binary orbital cycle than those requested in the main proposal. Data are requested on the whole FOV in particular to study the possible diffuse background emission from the Carina nebula. =========================================================================== ================== RFC 822 Headers ================== Return-Path: rauw@astra.astro.ulg.ac.be Received: by mssla3.mssl.ucl.ac.uk (UCX V4.1-12, OpenVMS V7.1 Alpha); Thu, 31 Jul 1997 18:43:05 +0100 Received: from aix4.segi.ulg.ac.be (msslr1.mssl.ucl.ac.uk [128.40.70.245]) by msslaa.mssl.ucl.ac.uk (8.8.6/8.8.6) with ESMTP id SAA16332 for ; Thu, 31 Jul 1997 18:43:05 +0100 (BST) Received: from arachnos.astro.ulg.ac.be (arachnos.astro.ulg.ac.be [139.165.20.60]) by aix4.segi.ulg.ac.be (8.8.4/8.6.10) with ESMTP id TAA83424 for ; Thu, 31 Jul 1997 19:43:02 +0200 Received: from astra.astro.ulg.ac.be (astra.astro.ulg.ac.be [139.165.20.2]) by arachnos.astro.ulg.ac.be (8.8.5/) with SMTP id TAA11067 for ; Thu, 31 Jul 1997 19:43:02 +0200 (MET DST) Received: by astra.astro.ulg.ac.be (4.1/SMI-4.1) id AA09036; Thu, 31 Jul 97 19:43:32 +0200 Date: Thu, 31 Jul 97 19:43:32 +0200 From: rauw@astra.astro.ulg.ac.be (Gregor Rauw) Message-Id: <9707311743.AA09036@astra.astro.ulg.ac.be> To: XMMOM_GTO@mssl.ucl.ac.uk Subject: Proposal WR22 apastron Cc: Panoptix@astra.astro.ulg.ac.be