124 research outputs found
Dusty Sources at the Galactic Center: The N- and Q-band view with VISIR
We present mid-infrared N- and Q-band photometry of the Galactic Center from
images obtained with the mid-infrared camera VISIR at the ESO VLT in May 2004.
The high resolution and sensitivity possible with VISIR enables us to
investigate a total of over 60 point-like sources, an unprecedented number for
the Galactic Center at these wavelengths. Combining these data with previous
results at shorter wavelengths (Viehmann et al. 2005) enables us to construct
SEDs covering the H- to Q-band regions of the spectrum, i.e. 1.6 to 19.5
m. We find that the SEDs of certain types of Galactic Center sources show
characteristic features. We can clearly distinguish between luminous Northern
Arm bow-shock sources, lower luminosity bow-shock sources, hot stars, and cool
stars. This characterization may help clarify the status of presently
unclassified sources.Comment: 18 pages, 4 figures, 1 table, accepted for publication in the
Astrophysical Journa
The Magnetic Field in the central parsec of the Galaxy
We present a polarisation map of the warm dust emission from the minispiral
in the central parsec of the Galactic centre. The observations were made at a
wavelength of 12.5 microns with CanariCam mounted on the 10.4-m Gran Telescopio
Canarias. The magnetic field traced by the polarised emission from aligned dust
grains is consistent with previous observations, but the increased resolution
of the present data reveals considerably more information on the detailed
structure of the B field and its correspondence with the filamentary emission
seen in both mid-infrared continuum emission and free-free emission at cm
wavelengths. The magnetic field appears to be compressed and pushed by the
outflows from luminous stars in the Northern Arm, but it is not disordered by
them. We identify some magnetically coherent filaments that cross the Northern
Arm at a Position Angle of ~45 degrees, and which may trace orbits inclined to
the primary orientation of the Northern Arm and circumnuclear disk. In the
East-West bar, the magnetic fields implied by the polarization in the lower
intensity regions lie predominantly along the bar at a Position Angle of 130 -
140 degrees. In contrast to the Northern Arm, the brighter regions of the bar
tend to have lower degrees of polarization with a greater divergence in
position angle compared to the local diffuse emission. It appears that the
diffuse emission in the East-West bar traces the underlying field and that the
bright compact sources are unrelated objects presumably projected onto the bar
and with different field orientationsComment: 12 Pages, 5 figures, 1 Table. To be published in MNRA
Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre I. Catalog of Variable Sources
We used four-year baseline HST/WFC3 IR observations of the Galactic Centre in
the F153M band (1.53 micron) to identify variable stars in the central
~2.3'x2.3' field. We classified 3845 long-term (periods from months to years)
and 76 short-term (periods of a few days or less) variables among a total
sample of 33070 stars. For 36 of the latter ones, we also derived their periods
(<3 days). Our catalog not only confirms bright long period variables and
massive eclipsing binaries identified in previous works, but also contains many
newly recognized dim variable stars. For example, we found \delta Scuti and RR
Lyrae stars towards the Galactic Centre for the first time, as well as one BL
Her star (period < 1.3 d). We cross-correlated our catalog with previous
spectroscopic studies and found that 319 variables have well-defined stellar
types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant
branch stars. We used colours and magnitudes to infer the probable variable
types for those stars without accurately measured periods or spectroscopic
information. We conclude that the majority of unclassified variables could
potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source
catalog will be valuable for future studies aimed at constraining the distance,
star formation history and massive binary fraction of the Milky Way nuclear
star cluster.Comment: has been accepted to be published in MNRAS, 64 pages, 26 figures. The
complete lists of table 3, 4, 8 and 9 will be published onlin
GRAVITY Spectro-interferometric Study of the Massive Multiple Stellar System HD 93206 A
Characterization of the dynamics of massive star systems and the astrophysical properties of the interacting components are a prerequisite for understanding their formation and evolution. Optical interferometry at milliarcsecond resolution is a key observing technique for resolving high-mass multiple compact systems. Here, we report on Very Large Telescope Interferometer/GRAVITY, Magellan/Folded-port InfraRed Echellette, and MPG2.2 m/FEROS observations of the late-O/early-B type system HD 93206 A, which is a member of the massive cluster Collinder 228 in the Carina nebula complex. With a total mass of about , it is one of the most compact massive quadruple systems known. In addition to measuring the separation and position angle of the outer binary Aa–Ac, we observe Brγ and He i variability in phase with the orbital motion of the two inner binaries. From the differential phase () analysis, we conclude that the Brγ emission arises from the interaction regions within the components of the individual binaries, which is consistent with previous models for the X-ray emission of the system based on wind–wind interaction. With an average 3σ deviation of , we establish an upper limit of p ~ 0.157 mas (0.35 au) for the size of the Brγ line-emitting region. Future interferometric observations with GRAVITY using the 8 m Unit Telescopes will allow us to constrain the line-emitting regions down to angular sizes of 20 μas (0.05 au at the distance of the Carina nebula)
SINFONI in the Galactic Center: young stars and IR flares in the central light month
We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the
central 30 light days of the Galactic Center [...]. To a limiting magnitude of
K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7
arcsec from the central black hole have spectral properties of B0-B9, main
sequence stars. [...] all brighter early type stars have normal rotation
velocities, similar to solar neighborhood stars. We [...] derive improved 3d
stellar orbits for six of these S-stars in the central 0.5 arcsec. Their
orientations in space appear random. Their orbital planes are not co-aligned
with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We
can thus exclude [...] that the S-stars as a group inhabit the inner regions of
these disks. They also cannot have been located/formed in these disks [...].
[...] we conclude that the S-stars were most likely brought into the central
light month by strong individual scattering events. The updated estimate of
distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32
kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We
happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum
spectral energy distributions of these flares are fit by a featureless, red
power law [...]. The observed spectral slope is in good agreement with
synchrotron models in which the infrared emission comes from [...] radiative
inefficient accretion flow in the central R~10 Rs region.Comment: 50 pages, 10 figures, 2 tables, submitted to ApJ, February 6th, 2005,
abstract abridge
Constraining scalar fields with stellar kinematics and collisional dark matter
The existence and detection of scalar fields could provide solutions to
long-standing puzzles about the nature of dark matter, the dark compact objects
at the centre of most galaxies, and other phenomena. Yet, self-interacting
scalar fields are very poorly constrained by astronomical observations, leading
to great uncertainties in estimates of the mass and the
self-interacting coupling constant of these fields. To counter this,
we have systematically employed available astronomical observations to develop
new constraints, considerably restricting this parameter space. In particular,
by exploiting precise observations of stellar dynamics at the centre of our
Galaxy and assuming that these dynamics can be explained by a single boson
star, we determine an upper limit for the boson star compactness and impose
significant limits on the values of the properties of possible scalar fields.
Requiring the scalar field particle to follow a collisional dark matter model
further narrows these constraints. Most importantly, we find that if a scalar
dark matter particle does exist, then it cannot account for both the
dark-matter halos and the existence of dark compact objects in galactic nucleiComment: 23 pages, 8 figures; accepted for publication by JCAP after minor
change
Status of research and development of vaccines for Streptococcus pyogenes.
Streptococcus pyogenes is an important global pathogen, causing considerable morbidity and mortality, especially in low and middle income countries where rheumatic heart disease and invasive infections are common. There is a number of promising vaccine candidates, most notably those based on the M protein, the key virulence factor for the bacterium. Vaccines against Streptococcus pyogenes are considered as impeded vaccines because of a number of crucial barriers to development. Considerable effort is needed by key players to bring current vaccine candidates through phase III clinical trials and there is a clear need to develop a roadmap for future development of current and new candidates
Архетип свобода у контексті французької політичної теорії та історії
Розглянуто сучасні підходи щодо аналізу політичної ментальності. У межах політологічного аналізу окреслено коло проблем, які потребують вирішення з використанням підходів психології. Зроблено висновок про те, що архетип “свобода” становить важливий елемент політичної ментальності французів.Modern approaches of analysis of political mentality are considered. Within the limits of political science analysis outlined circle of problems which need decision with the use of approaches of psychology. A conclusion is done that archetype freedom makes the important element of political mentality of French’s
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