We report the discovery of new Herbig–Haro (HH) jets in the Carina Nebula, and we discuss the protostellar outflow activity of a young OB association. These are the first results of an Hα imaging ...survey of Carina conducted with the Hubble Space Telescope (HST)/Advanced Camera for Surveys. Adding to the one previously known example (HH 666), we detect 21 new HH jets, plus 17 new candidate jets, ranging in length from 0.005 to 3 pc. Using the Hα emission measure to estimate jet densities, we derive jet mass-loss rates ranging from 8 × 10−9 to ∼10−6 M⊙ yr−1, but a comparison to the distribution of jet mass-loss rates in Orion suggests that we may be missing a large fraction of the jets below 10−8 M⊙ yr−1. A key qualitative result is that even some of the smallest dark globules with sizes of ≲1 arcsec (0.01 pc) are active sites of ongoing star formation because we see HH jets emerging from them, and that these offer potential analogues to the cradle of our Solar system because of their proximity to dozens of imminent supernovae that will enrich them with radioactive nuclides like 60Fe. Although most proplyd candidates identified from ground-based data are dark cometary globules, HST images now reveal proplyd structures in the core of the Tr 14 cluster, only 0.1–0.2 pc from several extreme O-type stars. Throughout Carina, some HH jets have axes bent away from nearby massive stars, while others show no bend, and still others are bent toward the massive stars. These jet morphologies serve as ‘wind socks’; strong photoevaporative flows can shape the jets, competing with the direct winds and radiation from massive stars. We find no clear tendency for jets to be aligned perpendicular to the axes of dust pillars. Finally, even allowing for a large number of jets that may escape detection, we find that HH jets are negligible to the global turbulence of the surrounding region, which is driven by massive star feedback.
Spectral classification of O2-3.5 If/WN5-7 stars Crowther, Paul A.; Walborn, Nolan R.
Monthly Notices of the Royal Astronomical Society,
September 2011, Letnik:
416, Številka:
2
Journal Article
Recenzirano
Odprti dostop
An updated classification scheme for transition O2-3.5 If*/WN5-7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2-3.5 If*, O2-3.5 ...If*/WN5-7 and WN5-7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2-3.5 If* stars in addition to the usual diagnostics from Walborn et al.; P Cygni for O2-3.5 If*/WN5-7 stars; purely in emission for WN stars in addition to the usual diagnostics from Smith et al. We also discuss approximate criteria to discriminate between these subtypes from near-infrared spectroscopy. The physical and wind properties of such stars are qualitatively discussed together with their evolutionary significance. We suggest that the majority of O2-3.5 If*/WN5-7 stars are young, very massive hydrogen-burning stars, genuinely intermediate between O2-3.5 If* and WN5-7 subtypes, although a minority are apparently core helium-burning stars evolving blueward towards the classical WN sequence. Finally, we reassess classifications for stars exhibiting lower ionization spectral features plus Hβ emission.
ABSTRACT An updated classification scheme for transition O2-3.5If*/WN5-7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2-3.5If*, ...O2-3.5If*/WN5-7 and WN5-7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2-3.5If* stars in addition to the usual diagnostics from Walborn et al.; P Cygni for O2-3.5If*/WN5-7 stars; purely in emission for WN stars in addition to the usual diagnostics from Smith et al. We also discuss approximate criteria to discriminate between these subtypes from near-infrared spectroscopy. The physical and wind properties of such stars are qualitatively discussed together with their evolutionary significance. We suggest that the majority of O2-3.5If*/WN5-7 stars are young, very massive hydrogen-burning stars, genuinely intermediate between O2-3.5If* and WN5-7 subtypes, although a minority are apparently core helium-burning stars evolving blueward towards the classical WN sequence. Finally, we reassess classifications for stars exhibiting lower ionization spectral features plus Hβ emission. PUBLICATION ABSTRACT
We present a catalog of relative proper motions for 368,787 stars in the 30 Doradus region of the Large Magellanic Cloud (LMC), based on a dedicated two-epoch survey with the Hubble Space Telescope ...and supplemented with proper motions from our pilot archival study. We demonstrate that a relatively short epoch difference of three years is sufficient to reach a level of precision of ∼0.1 mas yr−1 or better. A number of stars with relative proper motions exceeding a 3 error threshold represent a mixture of Milky Way denizens and 18 potential LMC runaway stars. Based upon 183 VFTS OB stars with the best proper motions, we conclude that none of them moves faster than ∼0.3 mas yr−1 in each coordinate-equivalent to ∼70 km s−1. Among the remaining 351 VFTS stars with less accurate proper motions, only one candidate OB runaway can be identified. We rule out any OB star in our sample moving at a tangential velocity exceeding ∼120 km s−1. The most significant result of this study is finding 10 stars over a wide range of masses that appear to have been ejected from the massive star cluster R136 in the tangential plane to angular distances from 35″ out to 407″, equivalent to 8-98 pc. The tangential velocities of these runaways appear to be correlated with apparent magnitude, indicating a possible dependence on the stellar mass. Lastly, a comparison to proper motions from Gaia DR 2 shows that for several relatively bright stars the DR 2 has an unexpected scatter that cannot be accounted for by the formal errors.
Galactic stars belonging to the Of?p category are all strongly magnetic objects exhibiting rotationally modulated spectral and photometric changes on timescales of weeks to years. Five candidate Of?p ...stars in the Magellanic Clouds have been discovered, notably in the context of ongoing surveys of their massive star populations. Here we describe an investigation of their photometric behaviour, revealing significant variability in all studied objects on timescales of one week to more than four years, including clearly periodic variations for three of them. Their spectral characteristics along with these photometric changes provide further support for the hypothesis that these are strongly magnetized O stars, analogous to the Of?p stars in the Galaxy.
The Of?p star CPD −28°2561 was monitored at high energies with XMM–Newton and HST. In X-rays, this magnetic oblique rotator displays bright and hard emission that varies by ∼55 per cent with ...rotational phase. These changes occur in phase with optical variations, as expected for magnetically confined winds; there are two maxima and two minima in X-rays during the 73 d rotational period of CPD −28°2561. However, contrary to previously studied cases, no significant hardness variation is detected between minima and maxima, with the exception of the second minimum which is slightly distinct from the first one. In the UV domain, broad-band fluxes remain stable while line profiles display large variations. Stronger absorptions at low velocities are observed when the magnetic equator is seen edge-on, which can be reproduced by a detailed 3D model. However, a difference in absorption at high velocities in the C iv and N v lines is also detected for the two phases where the confined wind is seen nearly pole-on. This suggests the presence of strong asymmetries about the magnetic equator, mostly in the free-flowing wind (rather than in the confined dynamical magnetosphere).
The most luminous Spitzer point sources in the 30 Doradus triggered second generation are investigated coherently in the 3-8 mu m region. Remarkable diversity and complexity in their natures are ...revealed. Some are also among the brightest JHK sources, while others are not. Several of them are multiple when examined at higher angular resolutions with Hubble Space Telescope NICMOS and WFPC2/WFC3 as available, or with VISTA/VMC otherwise. One is a dusty compact HII region near the far northwestern edge of the complex, containing a half-dozen bright I-band sources. Three others appear closely associated with luminous WN stars and causal connections are suggested. Some are in the heads of dust pillars oriented toward R136, as previously discussed from the NICMOS data. One resides in a compact cluster of much fainter sources, while another appears monolithic at the highest resolutions. Surprisingly, one is the brighter of the two extended "mystery spots" associated with Knot 2 of Walbom et al. Masses are derived from young stellar object models for unresolved sources and lie in the 10-30 M sub(middot in circle) range. Further analysis of the IR sources in this unique region will advance understanding of triggered massive star formation, perhaps in some unexpected and unprecedented ways.
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