The Be Star Newsletter, Volume 36 - October 2002

[Be Star Newsletter Home]

Exploiting the MSX Database Simon Clark1 & John M. Porter2 1University College London, Gower Street, London WC1E 6BT, UK email:  jsc@star.ucl.ac.uk 2Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD. UK email:  jmp@astro.livjm.ac.uk Received: 2002 September 26 We have used the first release of the data from the SPIRIT III instrument onboard the Midcourse Space Experiment (MSX, see Price et.al. 2001, for full details) to probe the galaxy and Magellanic Clouds for stars with mid-IR excesses indicative of the presence of circumstellar material. Here we briefly review initial results for the subset of bright blue stars that are likely Be, or related B[e] stars. MSX is a multidisciplinary experiment sponsored by the Ballistic Missile Defense Organization in the USA, and the SPIRIT III instrument (a 35cm off-axis telescope) was built at the Space Dynamics Laboratory at the Utah State University. MSX was launched on 24th April, 1996, with a mission lifetime of 5 years. A census of the Galactic plane using MSX has recently been completed by (Lumsden et.al. 2002). While the MSX data covers a smaller useable wavelength range (8.28-21.34µm) than IRAS and furthermore is somewhat less sensitive than IRAS at wavelengths 12µm (Table 1) the beam size, at 18.3'', is some 50 times smaller than that of IRAS at 12 & 25µm. Whilst the advantage of MSX over IRAS is mainly beam size, in the Plane, due to confusion and shadowing, the actual IRAS sensitivity at 12µm was about 3 Jy. For band A (8.28µm) there will be improved completeness over IRAS for sources between 100 mJy and 1 Jy. The motivation for this preliminary report is to encourage the hot star community to exploit this data set. Currently the first release of the data is online (v1.2), although v2.0 with better sensitivities will be available in late 2002. Table 1 ======================================== MSX band             (12µm)            v1.2               v2.0        ======================================== Band A                 8.28               0.1Jy          0.07Jy Band C               12.13                 1.2Jy                 0.5Jy Band D               14.66                 1.0Jy                 0.5Jy Band E                21.34               2-3Jy           1-1.5Jy ======================================== Central wavelengths and sensitivities for both v1.2 and v2.0 releases of the MSX PSC (v2.0 sensitivities provided by Dr. Mike Egan; MSX project scientist) Initially we have used the Bright Star Catalogue as our reference database. Positional (1) accuracy of the MSX PSC is expected to be ±1.5'' - we imposed upper limits on the offset between PSC and BSC of 4.5'' for possible detections. Following this procedure for the subset of ~1600 B stars in the BSC results in: there are 121 B type stars found with MSX in the galactic plane. of these 108 have detections at 8.28µm only. using the spectral type, the V magnitude, and the B-V colour from the BSC, a Kurucz model atmosphere (with redenning) can be assigned to each star. from the sample of 121 B stars, (at least) 16 show evidence for excess emission over the Kurucz photosphere model: these candidate Be stars include several well known sources such as  Cas, as well as three OB supergiants. 3 stars have evidence for warm dust detected at 12.13µm. These are HR7640 (HD189395, spectral type B9Vn) which may be a binary star, HR7699 (HD191243, spectral type B5Ib), and HR7983 (HD198625, spectral type B4Ve). As an illustration, below are the results for one star in particular: 48 Per. This star had detections at 12µm, 25µm and 60µm from IRAS which are also marked. The data are UBV from BSC and the JHK photometry (circles) from Howells et.al. (2001), MSX data (squares) and IRAS data (triangles). A simple Kurucz + f-f/b-f continuum model is fitted to the UBV and JHK photometry only. Given the increased spatial resolution over IRAS, the MSX PSC will provide a valuable resource for the quantitative analysis of both gaseous and dusty circumstellar envelopes around a wide variety of pre- to post-MS stellar objects (e.g. Clark & Porter; in preparation). We eagerly await the second release of the data. The MSX database is online ( http://www.ipac.caltech.edu/ipac/msx/msx.html). REFERENCES Howells L., Steele I.A., Porter J.M., & Etherton J., 2001 A&A, 369, 99 Lumsden S.L., Hoare M.G., Oudmaijer R.D., & Richards D., 2002 astro-ph/0206391 Price S.D., Egan M.P., Carey S.J., Mizuno D.R., & Kuchar T.A., 2001 AJ, 121, 2819