2,060 research outputs found
Near IR diffraction-limited integral-field SINFONI spectroscopy of the Circinus galaxy
Using the adaptive optics assisted near infrared integral field spectrometer
SINFONI on the VLT, we have obtained observations of the Circinus galaxy on
parsec scales. The morphologies of the H_2(1-0)S(1) 2.12um and Br_gamma 2.17um
emission lines are only slightly different, but their velocity maps are similar
and show a gradient along the major axis of the galaxy, consistent with
rotation.Since V_rot/sigma is approximately 1 suggests that random motions are
also important, it is likely that the lines arise in a rotating spheroid or
thickened disk around the AGN. Comparing the Br_gamma flux to the stellar
continuum indicates that the star formation in this region began almost 10^8 yr
ago. We also detect the [SiVI] 1.96um,[AlIX] 2.04um and [CaVIII] 2.32um coronal
lines. In all cases we observe a broad blue wing, indicating the presence of
two or more components in the coronal line region. A correlation between the
ionisation potential and the asymmetry of the profiles was found for these high
excitation species.Comment: 6 pages, 5 figures, Submitted to the Proceedings of the IFS Workshop,
Jul 4-8 2005, Durham, Englan
Near-Infrared spectroscopy of the super star cluster in NGC1705
We study the near-infrared properties of the super star cluster NGC1750-1 in
order to constrain its spatial extent, its stellar population and its age. We
use adaptive optics assisted integral field spectroscopy with SINFONI on the
VLT. We estimate the spatial extent of the cluster and extract its K-band
spectrum from which we constrain the age of the dominant stellar population.
Our observations have an angular resolution of about 0.11", providing an upper
limit on the cluster radius of 2.85+/-0.50 pc depending on the assumed
distance. The K-band spectrum is dominated by strong CO absorption bandheads
typical of red supergiants. Its spectral type is equivalent to a K4-5I star.
Using evolutionary tracks from the Geneva and Utrecht groups, we determine an
age of 12+/-6 Myr. The large uncertainty is rooted in the large difference
between the Geneva and Utrecht tracks in the red supergiants regime. The
absence of ionized gas lines in the K-band spectrum is consistent with the
absence of O and/or Wolf-Rayet stars in the cluster, as expected for the
estimated age.Comment: 5 pages, 4 figures. Research Note accepted in Astronomy and
Astrophysic
Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)
The 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. 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 explore 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 (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability
The orbit of the star S2 around SgrA* from VLT and Keck data
Two recent papers (Ghez et al. 2008, Gillessen et al. 2009) have estimated
the mass of and the distance to the massive black hole in the center of the
Milky Way using stellar orbits. The two astrometric data sets are independent
and yielded consistent results, even though the measured positions do not match
when simply overplotting the two sets. In this letter we show that the two sets
can be brought to excellent agreement with each other when allowing for a small
offset in the definition of the reference frame of the two data sets. The
required offsets in the coordinates and velocities of the origin of the
reference frames are consistent with the uncertainties given in Ghez et al.
(2008). The so combined data set allows for a moderate improvement of the
statistical errors of mass of and distance to Sgr A*, but the overall
accuracies of these numbers are dominated by systematic errors and the
long-term calibration of the reference frame. We obtain R0 = 8.28 +- 0.15(stat)
+- 0.29(sys) kpc and M(MBH) = 4.30 +- 0.20(stat) +- 0.30(sys) x 10^6 Msun as
best estimates from a multi-star fit.Comment: submitted to ApJ
NGC 3603 - a Local Template for Massive Young Clusters
We present a study of the star cluster associated with the massive Galactic
HII region NGC3603 based on near-IR broad-- and narrowband observations taken
with ISAAC/VLT under excellent seeing conditions (<0.4''). We discuss
color-color diagrams and address the impact of the high UV flux on the disk
evolution of the low-mass stars.Comment: 3 pages, 3 figures. To appear in the Proceedings of IAU Symposium 207
"Extragalactic Star Clusters", eds. E. Grebel, D. Geisler and D. Minitt
Performance of astrometric detection of a hotspot orbiting on the innermost stable circular orbit of the galactic centre black hole
The galactic central black hole Sgr A* exhibits outbursts of radiation in the
near infrared (so-called IR flares). One model of these events consists in a
hotspot orbiting on the innermost stable circular orbit (ISCO) of the hole.
These outbursts can be used as a probe of the central gravitational potential.
One main scientific goal of the second generation VLTI instrument GRAVITY is to
observe these flares astrometrically. Here, the astrometric precision of
GRAVITY is investigated in imaging mode, which consists in analysing the image
computed from the interferometric data. The capability of the instrument to put
in light the motion of a hotspot orbiting on the ISCO of our central black hole
is then discussed.
We find that GRAVITY's astrometric precision for a single star in imaging
mode is smaller than the Schwarzschild radius of Sgr A*. The instrument can
also demonstrate that a body orbiting on the last stable orbit of the black
hole is indeed moving. It yields a typical size of the orbit, if the source is
as bright as m_K=14.
These results show that GRAVITY allows one to study the close environment of
Sgr A*. Having access to the ISCO of the central massive black hole probably
allows constraining general relativity in its strong regime. Moreover, if the
hotspot model is appropriate, the black hole spin can be constrained.Comment: 13 pages, 11 figures ; accepted by MNRA
GCIRS16SW: a massive eclipsing binary in the Galactic Center
We report on the spectroscopic monitoring of GCIRS16SW, an Ofpe/WN9 star and
LBV candidate in the central parsec of the Galaxy. SINFONI observations show
strong daily spectroscopic changes in the K band. Radial velocities are derived
from the HeI 2.112 um line complex and vary regularly with a period of 19.45
days, indicating that the star is most likely an eclipsing binary. Under
various assumptions, we are able to derive a mass of ~ 50 Msun for each
component.Comment: 4 pages, 4 figures, ApJ Letters accepte
A polarised infrared flare from Sagittarius A* and the signatures of orbiting plasma hotspots
In this article we summarise and discuss the infrared, radio, and X-ray
emission from the supermassive black hole in the Galactic Centre, SgrA*. We
include new results from near-infrared polarimetric imaging observations
obtained on May 31st, 2006. In that night, a strong flare in Ks band (2.08
microns) reaching top fluxes of ~16 mJy could be observed. This flare was
highly polarised (up to ~40%) and showed clear sub-structure on a time scale of
15 minutes, including a swing in the polarisation angle of about 70 degrees.
For the first time we were able to observe both polarised flux and short-time
variability, with high significance in the same flare event. This result adds
decisive information to the puzzle of the SgrA* activity. The observed
polarisation angle during the flare peak is the same as observed in two events
in 2004 and 2005. Our observations strongly support the dynamical emission
model of a decaying plasma hotspot orbiting SgrA* on a relativistic orbit. The
observed polarisation parameters and their variability with time might allow to
constrain the orientation of accretion disc and spin axis with respect to the
Galaxy.Comment: 9 pages, 8 figures, accepted for publication in MNRA
LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT
LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner
camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric
main beam at 1.5 micron will be about 10 mas, offering unique imaging and
spectroscopic capabilities well beyond the angular resolution of current 8-10m
telescopes. At 10 mas angular scale, e.g., one resolution element at the
distance of the Galactic Center corresponds to the average diameter of the
Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of
the LBT interferometric beam with an equivalent maximum diameter of 23 m,
LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at
extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the
LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a
rather short timescale. The study investigates several concepts for the optical
as well as for the mechanical design. We present the scientific promises of
such an instrument together with the current status of the design study.Comment: 12 pages, SPIE conference proceeding, Orlando, 200
Near-Infrared-Spectroscopy with Extremely Large Telescopes: Integral-Field- versus Multi-Object-Instruments
Integral-field-spectroscopy and multi-object-spectroscopy provide the high
multiplex gain required for efficient use of the upcoming generation of
extremely large telescopes. We present instrument developments and designs for
both concepts, and how these designs can be applied to cryogenic near-infrared
instrumentation. Specifically, the fiber-based concept stands out the
possibility to expand it to any number of image points, and its modularity
predestines it to become the new concept for multi-field-spectroscopy. Which of
the three concepts --- integral-field-, multi-object-, or
multi-field-spectroscopy --- is best suited for the largest telescopes is
discussed considering the size of the objects and their density on the sky.Comment: 8 pages, 4 figures (converted to bitmap), to appear in the
proceedings of the Workshop on Extremely Large Telescopes, Sweden, June 1-2,
1999, uses spie.sty (V0.91) and spiebib.bst (V0.91
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