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Register a new userA comprehensive search for stellar bowshock nebulae in the Milky Way: a catalog of 709 mid-infrared selected candidates
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Added by
Henry A. (Chip) Kobulnicky
Publication date
2016
fields
Physics
and research's language is
English
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We identify 709 arc-shaped mid-infrared nebula in 24 micron Spitzer Space Telescope or 22 micron Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 microns or shorter mid-infrared wavelengths as well. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near Galactic mid-Plane with an angular scale height of ~0.6 degrees. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate runaway stars potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess having velocity vectors aligned with the infrared morphology --- kinematic evidence that many of these are runaway stars with large peculiar motions responsible for the bowshock signature. We discuss a population of in-situ bowshocks (103 objects) that face giant HII regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify 58 objects that face 8 micron bright-rimmed clouds and apparently constitute a sub-class of in-situ bowshocks where the stellar wind interacts with a photo-evaporative flow from an eroding molecular cloud interface (i.e., PEF bowshocks). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as HII regions are responsible for producing some bowshock nebulae. However, the vast majority of this sample appear to be isolated (499 objects) from obvious external influences.
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Arcuate infrared nebulae are ubiquitous throughout the Galactic Plane and are candidates for partial shells, bubbles, or bowshocks produced by massive runaway stars. We tabulate infrared photometry for 709 such objects using images from the Spitzer Space Telescope (SST), Wide-Field Infrared Explorer (WISE), and Herschel Space Observatory (HSO). Of the 709 objects identified at 24 or 22 microns, 422 are detected at the HSO 70 micron bandpass. Of these, only 39 are detected at HSO 160 microns. The 70 micron peak surface brightnesses are 0.5 to 2.5 Jy/square arcminute. Color temperatures calculated from the 24 micron to 70 micron ratios range from 80 K to 400 K. Color temperatures from 70 micron to 160 micron ratios are systematically lower, 40 K to 200 K. Both of these temperature are, on average, 75% higher than the nominal temperatures derived by assuming that dust is in steady-state radiative equilibrium. This may be evidence of stellar wind bowshocks sweeping up and heating --- possibly fragmenting but not destroying --- interstellar dust. Infrared luminosity correlates with standoff distance, R_0, as predicted by published hydrodynamical models. Infrared spectral energy distributions are consistent with interstellar dust exposed to a either single radiant energy density, U=10^3 to 10^5 (in more than half of the objects) or a range of radiant energy densities U_min=25 to U_max=10^3 to 10^5 times the mean interstellar value for the remainder. Hence, the central OB stars dominate the energetics, making these enticing laboratories for testing dust models in constrained radiation environments. SEDs are consistent with PAH fractions q_PAH <1% in most objects.
We present an open-access database which includes a synthetic catalog of black holes in the Milky Way. To calculate evolution of single and binary stars we used updated population synthesis code StarTrack. We applied a new model of star formation history and chemical evolution of Galactic disk, bulge and halo synthesized from observational and theoretical data. We find that at the current moment Milky Way (disk+bulge+halo) contains about 1.2 x 10^8 single black holes with average mass of about 14 Msun and 9.3 x 10^6 BHs in binary systems with average mass of 19 Msun. We present basic statistical properties of BH populations such as distributions of single and binary BH masses, velocities, orbital parameters or numbers of BH binary systems in different evolutionary configurations. We find that the most massive BHs are formed in mergers of binary systems, such as BH-MS, BH+He, BH-BH. The metallicity of stellar population has a significant impact on the final BH mass due to the stellar winds. Therefore the most massive single BH in our simulation, 113 Msun, originates from a merger of a helium star and a black hole in a low metallicity stellar environment in Galactic halo. The most massive BH in binary system is 60 Msun and was also formed in Galactic halo. We constrain that only 0.006% of total Galactic halo mass (including dark matter) could be hidden in the form of stellar origin BHs which are not detectable by current observational surveys. Galactic binary BHs are minority (10% of all Galactic BHs) and most of them are in BH-BH systems. The current Galactic merger rates for two considered common envelope models which are: 3-81 Myr^-1 for BH-BH, 1-9 Myr^-1, for BH-NS and 14-59 Myr^-1 for NS-NS systems. Data files are available at https://bhc.syntheticuniverse.org/.
We present the Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC) dedicated to long-baseline interferometry at mid-infrared wavelengths (3-13 mum). It gathers data for half a million stars, i.e. nearly all the stars of the Hipparcos-Tycho catalogue whose spectral type is reported in the SIMBAD database. We cross-match 26 databases to provide basic information, binarity elements, angular diameter, magnitude and flux in the near and mid-infrared, as well as flags that allow us to identify the potential calibrators. The catalogue covers the entire sky with 465 857 stars, mainly dwarfs and giants from B to M spectral types closer than 18 kpc. The smallest reported values reach 0.16 muJy in L and 0.1 muJy in N for the flux, and 2 microarcsec for the angular diameter. We build 4 lists of calibrator candidates for the L- and N-bands suitable with the Very Large Telescope Interferometer (VLTI) sub- and main arrays using the MATISSE instrument. We identify 1 621 candidates for L and 44 candidates for N with the Auxiliary Telescopes (ATs), 375 candidates for both bands with the ATs, and 259 candidates for both bands with the Unit Telescopes (UTs). Predominantly cool giants, these sources are small and bright enough to belong to the primary lists of calibrator candidates. In the near future, we plan to measure their angular diameter with 1% accuracy.
We present high-resolution Magellan/MIKE spectra of 22 bright ($9<V<13.5$) metal-poor stars ($-3.18<mbox{[Fe/H]}<-1.37$) in three different stellar streams, the Helmi debris stream, the Helmi trail stream, and the $omega$ Centauri progenitor stream. We augment our Helmi debris sample with results for ten stars by Roederer et al. 2010 (arXiv:1001.1745), for a total of 32 stars. Detailed chemical abundances of light elements as well as heavy neutron-capture elements have been determined for our 22 stars. All three streams contain carbon-enhanced stars. For 13 stars, neutron-capture element lines were detectable and they all show signatures in agreement with the scaled solar $r$-process pattern, albeit with a large spread of $-0.5<mbox{[Eu/Fe]}<+1.3$. Eight of these stars show an additional small $s$-process contribution superposed onto their $r$-process pattern. This could be discerned because of the relatively high $S/N$ of the spectra given that the stars are close by in the halo. Our results suggest that the progenitors of these streams experienced one or more $r$-process events, such as a neutron star merger or another prolific $r$-process source, early on that widely enriched these host systems before their accretion by the Milky Way. The small $s$-process contribution suggests the presence of AGB stars and associated local (inhomogeneous) enrichment as part of the ongoing chemical evolution by low mass stars. Stars in stellar streams may thus be a promising avenue for studying the detailed history of large dwarf galaxies and their role in halo assembly with easily accessible targets for high-quality spectra of many stars.
We study the line widths in the [ion{O}{3}]$lambda$5007 and H$alpha$ lines for two groups of planetary nebulae in the Milky Way bulge based upon spectroscopy obtained at the Observatorio Astronomico Nacional in the Sierra San Pedro Martir (OAN-SPM) using the Manchester Echelle Spectrograph. The first sample includes objects early in their evolution, having high H$beta$ luminosities, but [ion{O}{3}]$lambda 5007/mathrm Hbeta < 3$. The second sample comprises objects late in their evolution, with ion{He}{2} $lambda 4686/mathrm Hbeta > 0.5$. These planetary nebulae represent evolutionary phases preceeding and following those of the objects studied by Richer et al. (2008). Our sample of planetary nebulae with weak [ion{O}{3}]$lambda$5007 has a line width distribution similar to that of the expansion velocities of the envelopes of AGB stars, and shifted to systematically lower values as compared to the less evolved objects studied by Richer et al. (2008). The sample with strong ion{He}{2} $lambda 4686$ has a line width distribution indistinguishable from that of the more evolved objects from Richer et al. (2008), but a distribution in angular size that is systematically larger and so they are clearly more evolved. These data and those of Richer et al. (2008) form a homogeneous sample from a single Galactic population of planetary nebulae, from the earliest evolutionary stages until the cessation of nuclear burning in the central star. They confirm the long-standing predictions of hydrodynamical models of planetary nebulae, where the kinematics of the nebular shell are driven by the evolution of the central star.
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