51,843 research outputs found
The Ionizing Stars of the Galactic Ultra-Compact HII Region G45.45+0.06
Using the NIFS near-infrared integral-field spectrograph behind the facility
adaptive optics module, ALTAIR, on Gemini North, we have identified several
massive O-type stars that are responsible for the ionization of the Galactic
Ultra-Compact HII region G45.45+0.06. The sources ``m'' and ``n'' from the
imaging study of Feldt et a. 1998 are classified as hot, massive O-type stars
based on their K-band spectra. Other bright point sources show red and/or
nebular spectra and one appears to have cool star features that we suggest are
due to a young, low-mass pre-main sequence component. Still two other embedded
sources (``k'' and ``o'' from Feldt et al.) exhibit CO bandhead emission that
may arise in circumstellar disks which are possibly still accreting. Finally,
nebular lines previously identified only in higher excitation planetary nebulae
and associated with KrIII and SeIV ions are detected in G45.45+0.06.Comment: Latex, 28 pages, 10 figure
The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge
Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron
continuum) band filters are used to investigate the photometric properties of
bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex.
The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude
diagrams are well matched by the Baade's Window (BW) M giant sequence if the
mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars
are estimated using the M_K versus infrared color relations defined by M giants
in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The
extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag.
Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J,
H, and K brightnesses, and over 5300 stars with H and K brightnesses. The
distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be
reproduced using the M_K versus CO_o relation defined by M giants in BW. The
data thus suggest that the most metal-rich giants in the central regions of the
bulge and in BW have similar photometric properties and 2.3micron CO strengths.
Hence, it appears that the central region of the bulge does not contain a
population of stars that are significantly more metal-rich than what is seen in
BW.Comment: 29 pages, including 14 figure
The Stellar Content Near the Galactic Center
High angular resolution J, H, K, and L' images are used to investigate the
stellar content within 6 arcsec of SgrA*. The data, which are complete to K ~
16, are the deepest multicolor observations of the region published to date.Comment: 34 pages, including 12 figure
Why don't clumps of cirrus dust gravitationally collapse?
We consider the Herschel-Planck infrared observations of presumed
condensations of interstellar material at a measured temperature of
approximately 14 K (Juvela et al., 2012), the triple point temperature of
hydrogen. The standard picture is challenged that the material is cirrus-like
clouds of ceramic dust responsible for Halo extinction of cosmological sources
(Finkbeiner, Davis, and Schlegel 1999). Why would such dust clouds not collapse
gravitationally to a point on a gravitational free-fall time scale of
years? Why do the particles not collide and stick together, as is fundamental
to the theory of planet formation (Blum 2004; Blum and Wurm, 2008) in pre-solar
accretion discs? Evidence from 3.3 m and UIB emissions as well as ERE
(extended red emission) data point to the dominance of PAH-type macromolecules
for cirrus dust, but such fractal dust will not spin in the manner of rigid
grains (Draine & Lazarian, 1998). IRAS dust clouds examined by Herschel-Planck
are easily understood as dark matter Proto-Globular-star-Cluster (PGC) clumps
of primordial gas planets, as predicted by Gibson (1996) and observed by Schild
(1996).Comment: 8 pages, 2 figures, Conference FQMT'1
Philomen Schönhagen & Mike Meißner. Kommunikations- und Mediengeschichte. Von Versammlungen bis zu den digitalen Medien
Philomen Schönhagen legt zusammen mit Mike Meißner eine Kommunikations- und Mediengeschichte vor, die den Fokus vor allem auf die Schweiz legt. Das fehlte bisher. Es gibt Medien- und Journalismusgeschichten Frankreichs, Deutschlands, Italiens, weltweit, es gibt das Handbuch der Mediengeschichte von Helmut Schanze, aber an eine Gesamtschau für die Schweiz hat sich seit langem niemand gewagt.
Philomen Schönhagen, avec l’aide de Mike Meißner, propose une histoire de la communication et des médias qui met l’accent sur la Suisse. Cela manquait jusque-là . Il existe des histoires des médias et du journalisme en France, en Allemagne, en Italie et dans le monde entier, il y a le manuel d’histoire des médias de Helmut Schlanze, mais il y avait longtemps que personne n’avait tenté de livrer une vue d’ensemble de la situation en Suisse.
Philomen Schönhagen, insieme a Mike Meißner, presenta per la prima volta una ricerca sulla storia della comunicazione e dei media incentrata principalmente sulla Svizzera. Fino ad oggi esistono studi sulla storia dei media e del giornalismo in Francia, Germania, Italia e a nivello mondiale, oltre al manuale sulla storia dei media di Helmut Schanze
The Stellar Content of Obscured Galactic Giant H II Regions III.: W31
We present near infrared (J, H, and K) photometry and moderate resolution
(lambda/Deltalambda = 3000) K-band spectroscopy of the embedded stellar cluster
in the giant H II region W31. Four of the brightest five cluster members are
early O--type stars based on their spectra. We derive a spectro--photometric
distance for W31 of 3.4 +/- 0.3 kpc using these new spectral types and infrared
photometry. The brightest cluster source at K is a red object which lies in the
region of the J - H vs. H - K color--color plot inhabited by stars with excess
emission in the K-band. This point source has an H plus K-band spectrum which
shows no photospheric features, which we interpret as being the result of
veiling by local dust emission. Strong Brackett series emission and permitted
FeII emission are detected in this source; the latter feature is suggestive of
a dense inflow or outflow. The near infrared position of this red source is
consistent with the position of a 5 GHz thermal radio source seen in previous
high angular resolution VLA images. We also identify several other K-band
sources containing excess emission with compact radio sources. These objects
may represent stars in the W31 cluster still embedded in their birth cocoons.Comment: LaTeX2e/aastex, 29 pages including 9 figures, 3 table
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