Abstract
We present the first results of a study of the stellar population in a region of 30 pc radius around SN 1987A, based on an analysis of multiband Hubble Space Telescope (HST) WFPC2 images. The effective temperature, radius and, possibly, reddening of each star were determined by fitting the measured broadband magnitudes to the ones calculated with model atmospheres. In particular, we have determined effective temperatures and bolometric luminosities for 21,995 stars, and for a subsample of 2510 stars we also determined individual reddening corrections. In addition, we have identified all stars with H? equivalent widths in excess of 8 ?, a total of 492 stars. An inspection of the H-R diagram reveals the presence of several generations of young stars, with ages between 1 and 150 Myr, superposed on a much older field population (0.6-6 Gyr). A substantial fraction of young stars with ages around 12 Myr make up the stellar generation coeval to SN 1987A progenitor. The youngest stars in the field appear to be strong-line T Tauri stars, identified on the basis of their conspicuous (Weq > 8 ?) H? excesses. This constitute the first positive detection of low-mass (about 1-2 M?) pre-main-sequence (PMS) stars outside the Milky Way. Their positions in the H-R diagram appear to require that star formation in the LMC occurs with accretion rates about 10 times higher than in the Milky Way, i.e., ~10-4 M? yr-1. SN 1987A appears to belong to a loose, young cluster 12 ? 2 Myr old, in which the slope of the present mass function is almost identical to Salpeter's, i.e., ? = d log N/d log M -1.25 for masses above 3 M?, but becomes much flatter for lower masses, i.e., ? -0.5. On a large scale, we find that the spatial distributions of massive stars and low-mass PMS stars are conclusively different, indicating that different star formation processes operate for high- and low-mass stars. This results casts doubts on the validity of an initial mass function (IMF) concept on a small scale (say, less than 10 pc). Moreover, it appears that a determination of the low-mass end IMF in the LMC requires an explicit identification of PMS stars. A preliminary analysis, done for the whole field as a single entity, shows that the IMF slope for the young population present over the entire region is steeper than ? -1.7.
Highlights
SN 1987A has been one of the Ðrst targets ever observed with the Hubble Space T elescope (HST )
SN 1987A caught everybodyÏs eye with its beautiful triple ring circumstellar nebula, which was imaged with the new WFPC2 (Burrows et al 1995 ; Panagia et al 1996)
initial mass function (IMF) with slope ! in the range [1 to [2, we estimate that the cluster originally included additional 2 ^ 1 stars in the mthaesSsNran19g8e72A0Èe8v0enMt._H, owwheicvhere,xtphleordeeids as SN II no clear well sign before of any shelllike structure centered on the cluster
Summary
SN 1987A has been one of the Ðrst targets ever observed with the Hubble Space T elescope (HST ). Kirshner) project to monitor the evolution of the supernova as well as the changes in the emission of the rings The combination of these images, always centered on the supernova but taken with di†erent roll angles, resulted in an excellent coverage of an area of about 130A radius, i.e., about 30 pc, around SN 1987A. PreÈmain-sequence (PMS) Their detection provides an stars excellent tracing of the low mass PMS star spatial distribution, which is compared with that of coeval, more massive stars. On this basis, we show that within the stellar generation of SN 1987A the more grouped around the massive stars We consider and discuss the problem of determining the initial mass function (IMF), concluding that an explicit identiÐcation of PMS stars based on spectroscopic criteria is absolutely necessary to separate young, low-mass stars from older population, Ðeld stars properly
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.