1,506 research outputs found
Preflight SL-1/SL-3 Skylab VHF ranging coverage (nominal TPI). Antenna and propagation studies for spacecraft systems, task E-531
A preflight assessment of the Skylab VHF ranging coverage for the rendezvous portion of the nominal SL-1/SL-3 mission is reported, assuming a 27 July 1973 SL-3 launch. Data are based on a nominal attitude trajectory, which has the Saturn workshop in a solar inertial attitude throughout the rendezvous; the CSM terminal phase initiation maneuver is nominal. An addendum to this report is being prepared, which considers the effects of early and late TPI maneuvers. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 600 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function
Antenna and propagation studies for spacecraft systems: Addendum to preflight SL-1/SL-3 Skylab VHF ranging coverage (early and late TPI)
A preflight assessment is presented of the expected Skylab VHF ranging coverage for the rendezvous portion of the SL-1/SL-3 mission, assuming a 28 July 1973 launch date, for the alternative trajectory cases characterized by either an early TPI or a late TPI. In this assessment early TPI and late TPI are used to indicate a TPI maneuver occurring 10 minutes prior to or after the nominally scheduled TPI maneuver, respectively. The Saturn workshop (SWS) maintains a solar inertial (SI) attitude throughout rendezvous for both trajectory cases. The results summarized concern VHF ranging function performance during that period most likely to be affected by off-nominal TPI conditions, i.e., NSR (5:56 g.e.t.) to station keeping. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 100 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function
Intense Star-formation and Feedback at High Redshift: Spatially-resolved Properties of the z=2.6 Submillimeter Galaxy SMMJ14011+0252
We present a detailed analysis of the spatially-resolved properties of the
lensed submillimeter galaxy SMMJ14011+0252 at z=2.56, combining deep
near-infrared integral-field data obtained with SPIFFI on the VLT with other
multi-wavelength data sets. The broad characteristics of SMMJ14011+0252 are in
agreement with what is expected for the early evolution of local massive
spheroidal galaxies. From continuum and line flux, velocity, and dispersion
maps, we measure the kinematics, star-formation rates, gas densities, and
extinction for individual subcomponents. The star formation intensity is
similar to low-redshift ``maximal starbursts'', while the line fluxes and the
dynamics of the emission line gas provide direct evidence for a
starburst-driven wind with physical properties very similar to local
superwinds. We also find circumstantial evidence for "self-regulated" star
formation within J1. The relative velocity of the bluer companion J2 yields a
dynamical mass estimate for J1 within about 20 kpc, M_dyn \sim 1\times 10^{11}
M_sun. The relative metallicity of J2 is 0.4 dex lower than in J1n/s,
suggesting different star formation histories. SED fitting of the continuum
peak J1c confirms and substantiates previous suggestions that this component is
a z=0.25 interloper. When removing J1c, the stellar continuum and H-alpha line
emission appear well aligned spatially in two individual components J1n and
J1s, and coincide with two kinematically distinct regions in the velocity map,
which might well indicate a merging system. This highlights the close
similarity between SMGs and ULIRGs, which are often merger-driven maximal
starbursts, and suggests that the intrinsic mechanisms of star-formation and
related feedback are similar to low-redshift strongly star-forming systems.Comment: Some of the figures changed from b/w to colo
Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)
International audienceThe accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. However, biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to develop complementary SST proxies for these cool water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (?44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin) is strongly related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.04)? per 1°C highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that however in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C and salinity of 33.0 (±0.5)? a prominent shift in biomineralization affect the Ca isotope composition of N. pachyderma (sin.) becoming insensitive to temperature. These findings highlight the need of systematic calibration studies to unravel the influencing factors on Ca isotope fractionation and to validate the proxies' applicability
Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56
Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we
have studied the spatially-resolved dynamics in the z=3.2 strongly lensed
galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high
surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy
(seen at a spatial resolution of about 200 pc in the source plane), whereas the
fainter ``arc'' is a more strongly magnified peripheral region of the same
galaxy at about a half-light radius, which otherwise appears to be a typical
z=3 Lyman break galaxy.
The overall shape of the position-velocity diagram resembles the ``rotation
curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected
velocities rise rapidly to 75 km/s within the core. This implies a dynamical
mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this
system the equivalent of the mass of a present-day L* bulge at the same radius
was already in place by z>=3. Approximating the circular velocity of the halo
by the measured asymptotic velocity of the rotation curve, we estimate a dark
matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with
large-scale clustering studies of Lyman break galaxies. The baryonic collapse
fraction is low compared to actively star-forming ``BX'' and low-redshift
galaxies around z=2, perhaps implying comparatively less gas infall to small
radii or efficient feedback. Even more speculatively, the high central mass
density might indicate highly dissipative gas collapse in very early stages of
galaxy evolution, in approximate agreement with what is expected for
``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa
Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations
Aims. We report on simultaneous observations and modeling of mid-infrared
(MIR), near-infrared (NIR), and submillimeter (submm) emission of the source
Sgr A* associated with the supermassive black hole at the center of our Galaxy.
Our goal was to monitor the activity of Sgr A* at different wavelengths in
order to constrain the emitting processes and gain insight into the nature of
the close environment of Sgr A*. Methods. We used the MIR instrument VISIR in
the BURST imaging mode, the adaptive optics assisted NIR camera NACO, and the
sub-mm antenna APEX to monitor Sgr A* over several nights in July 2007.
Results. The observations reveal remarkable variability in the NIR and sub-mm
during the five nights of observation. No source was detected in the MIR, but
we derived the lowest upper limit for a flare at 8.59 microns (22.4 mJy with
A_8.59mu = 1.6+/- 0.5). This observational constraint makes us discard the
observed NIR emission as coming from a thermal component emitting at sub-mm
frequencies. Moreover, comparison of the sub-mm and NIR variability shows that
the highest NIR fluxes (flares) are coincident with the lowest sub-mm levels of
our five-night campaign involving three flares. We explain this behavior by a
loss of electrons to the system and/or by a decrease in the magnetic field, as
might conceivably occur in scenarios involving fast outflows and/or magnetic
reconnection.Comment: 10 pages, 7 figures, published in A&
SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution
We present 0.5" resolution near-IR integral field spectroscopy of the Ha line
emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT.
The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected
over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved
velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of
the larger systems are consistent with orbital motions. Four galaxies are well
described by rotating disks with clumpy morphologies and we extract rotation
curves out to radii > ~10kpc. One or two galaxies exhibit signatures more
consistent with mergers. Analyzing all 14 galaxies in the framework of rotating
disks, we infer mean inclination- and beam-corrected maximum circular
velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun
within r_1/2. On average, the dynamical masses are consistent with photometric
stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun
Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to
those of local late-type galaxies. The specific angular momenta of their
baryons are comparable to those of their dark matter halos. Extrapolating from
the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in
our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases
implies a ratio of v_c to local velocity dispersion of order 2-4 and
accordingly a large geometric thickness. We argue that this suggests a mass
accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue
that if our BM/BX galaxies were initially gas rich, their clumpy disks will
subsequently lose their angular momentum and form compact bulges on a timescale
of ~1 Gyr. [ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 17 pages, 5
color figure
Evidence for a Long-Standing Top-Heavy IMF in the Central Parsec of the Galaxy
We classify 329 late-type giants within 1 parsec of Sgr A*, using the
adaptive optics integral field spectrometer SINFONI on the VLT. These
observations represent the deepest spectroscopic data set so far obtained for
the Galactic Center, reaching a 50% completeness threshold at the approximate
magnitude of the helium-burning red clump (Ks ~ 15.5 mag.). Combining our
spectroscopic results with NaCo H and Ks photometry, we construct an observed
Hertzsprung-Russell diagram, which we quantitatively compare to theoretical
distributions of various star formation histories of the inner Galaxy, using a
chi-squared analysis. Our best-fit model corresponds to continuous star
formation over the last 12 Gyr with a top-heavy initial mass function (IMF).
The similarity of this IMF to the IMF observed for the most recent epoch of
star formation is intriguing and perhaps suggests a connection between recent
star formation and the stars formed throughout the history of the Galactic
Center.Comment: 18 pages, 10 figures, Accepted to ApJ: 15 July 200
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
Star formation in the central 0.5 pc of the Milky Way
The supermassive black hole candidate at the Galactic Center is surrounded by
a parsec-scale star cluster, which contains a number of early type stars. The
presence of such stars has been called a "paradox of youth" as star formation
in the immediate vicinity of a supermassive black hole seemed difficult, as
well as the transport of stars from far out in a massive-star lifetime. I will
recall 30 years of technological developments which led to the current
understanding of the nuclear cluster stellar population. The number of early
type stars known at present is sufficient to access the 3D structure of this
population and its dynamics, which in turn allows discriminating between the
various possible origins proposed along the years.Comment: 8 pages, invited review for the conference "The Universe under the
Microscope" (AHAR 2008), to be published in Journal of Physics: Conference
Series by Institute of Physics Publishin
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