Linear relation for wind-blown bubble sizes of main-sequence OB stars in a molecular environment and implication for supernova progenitors

We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R_b \approx 1.22M/Msun - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 Msun will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.Comment: 5 emulateapj pages, 1 figure, 2 tables. ApJ(Letters), 769, L16 (2013

The ISM Interactions of a Runaway LBV Nebula in the LMC

New observations of the Magellanic Cloud Luminous Blue Variable candidate S119 (HD269687) show the relationship of the star to its environs. Echelle spectroscopy and high-resolution HST imagery reveal an expanding bubble centered on the star. This bubble appears in both Halpha and [NII] and is noticeably brighter on the near (blue-shifted) side. The systemic velocity of both the expanding bubble and the star itself (as seen by the very broad Halpha emission feature in the stellar spectrum) is V_hel=160 km/s whereas the velocity of the superposed LMC ISM is 250-300 km/s. ISM absorption features seen in FUSE spectra reveal components at both stellar and LMC velocities. Thus we conclude that S119 is located within the LMC ISM and that the bubble is interacting strongly with the ISM in a bow shock.Comment: 5 pages in EmulateApJ format, 3 figures Accepted by ApJL See http://fuse.pha.jhu.edu/~danforth/s119

Star Formation in the LMC: Gravitational Instability and Dynamical Triggering

Evidence for triggered star formation is difficult to establish because energy feedback from massive stars tend to erase the interstellar conditions that led to the star formation. Young stellar objects (YSOs) mark sites of {\it current} star formation whose ambient conditions have not been significantly altered. Spitzer observations of the Large Magellanic Cloud (LMC) effectively reveal massive YSOs. The inventory of massive YSOs, in conjunction with surveys of interstellar medium, allows us to examine the conditions for star formation: spontaneous or triggered. We examine the relationship between star formation and gravitational instability on a global scale, and we present evidence of triggered star formation on local scales in the LMC.Comment: 6 pages, 6 figures, IAU Symposium 237, Triggered Star Formation in a Turbulent Medium, eds. Elmegreen and Palou

A Deep Chandra Observation of the Giant HII Region N11 I. X-ray Sources in the Field

A very sensitive X-ray investigation of the giant HII region N11 in the LMC was performed using the Chandra X-ray Observatory. The 300ks observation reveals X-ray sources with luminosities down to 10^32 erg/s, increasing by more than a factor of 5 the number of known point sources in the field. Amongst these detections are 13 massive stars (3 compact groups of massive stars, 9 O-stars and one early B-star) with log(Lx/Lbol)~-6.5 to -7, which may suggest that they are highly magnetic or colliding wind systems. On the other hand, the stacked signal for regions corresponding to undetected O-stars yields log(Lx/Lbol)~-7.3, i.e., an emission level comparable to similar Galactic stars despite the lower metallicity. Other point sources coincide with 11 foreground stars, 6 late-B/A stars in N11, and many background objects. This observation also uncovers the extent and detailed spatial properties of the soft, diffuse emission regions but the presence of some hotter plasma in their spectra suggests contamination by the unresolved stellar population.Comment: file including online material, accepted for publication by ApJ