40 research outputs found
MicroLux: high-precision timing of high-speed photometric observations
MicroLux is a GPS-based high precision and high speed timing add-on to the
Calar Alto Lucky Imaging camera AstraLux. It allows timestamping of individual
CCD exposures at frame rates of more than 1 kHz with an accuracy better than
one microsecond with respect to the UTC timeframe. The system was successfully
used for high speed observations of the optical pulse profile of the Crab
pulsar in January and November 2007. I present the technical design concept of
MicroLux as well as first results from these observations, in particular the
reconstructed pulse profile of the pulsar.Comment: 8 pages, 6 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200
AstraLux: the Calar Alto Lucky Imaging Camera
AstraLux is the Lucky Imaging camera for the Calar Alto 2.2-m telescope,
based on an electron-multiplying high speed CCD. By selecting only the best
1-10% of several thousand short exposure frames, AstraLux provides nearly
diffraction limited imaging capabilities in the SDSS i' and z' filters over a
field of view of 24x24 arcseconds. By choosing commercially available
components wherever possible, the instrument could be built in short time and
at comparably low cost. We present the instrument design, the data reduction
pipeline, and summarise the performance and characteristicsComment: 12 pages, 7 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200
Examining the T Tauri system with SPHERE
Context. The prototypical low-mass young stellar object, T Tauri, is a
well-studied multiple system with at least three components. Aims. We aim to
explore the T Tau system with the highest spatial resolution, study the time
evolution of the known components, and re-determine the orbital parameters of
the stars. Methods. Near-infrared classical imaging and integral field
spectrograph observations were obtained during the Science Verification of
SPHERE, the new high-contrast imaging facility at the VLT. The obtained FWHM of
the primary star varies between 0.050" and 0.059", making these the highest
spatial resolution near-infrared images of the T Tauri system obtained to date.
Results. Our near-infrared images confirm the presence of extended emission
south of T Tau Sa, reported in the literature. New narrow-band images show, for
the first time, that this feature shows strong emission in both the Br-{\gamma}
and H2 1-0 S(1) lines. Broadband imaging at 2.27 {\mu}m shows that T Tau Sa is
0.92 mag brighter than T Tau Sb, which is in contrast to observations from Jan.
2014 (when T Tau Sa was fainter than Sb), and demonstrates that T Tau Sa has
entered a new period of high variability. The newly obtained astrometric
positions of T Tau Sa and Sb agree with orbital fits from previous works. The
orbit of T Tau S (the center of gravity of Sa and Sb) around T Tau N is poorly
constrained by the available observations and can be fit with a range of orbits
ranging from a nearly circular orbit with a period of 475 years to highly
eccentric orbits with periods up to 2.7*10^4 years. We also detected a feature
south of T Tau N, at a distance of mas, which shows the properties
of a new companion.Comment: Accepted by A&A Letter
The AstraLux large M dwarf survey
AstraLux is the Lucky Imaging camera for the Calar Alto 2.2-m telescope and
the 3.5-m NTT at La Silla. It allows nearly diffraction limited imaging in the
SDSS i' and z' bands of objects as faint as i'=15.5mag with minimum technical
effort.
One of the ongoing AstraLux observing programs is a binarity survey among
late-type stars with spectral types K7 to M8, covering more than 1000 targets
on the northern and southern hemisphere. The survey is designed to refine
binarity statistics and especially the dependency of binarity fraction on
spectral type. The choice of the SDSS i' and z' filters allows to obtain
spectral type and mass estimates for resolved binaries.
With an observing efficiency of typically 6 targets per hour we expect to
complete the survey in mid-2009. Selected targets will be followed up
astrometrically and photometrically, contributing to the calibration of the
mass-luminosity relation at the red end of the main sequence and at visible
wavelengths.Comment: 4 pages, 3 figures. To appear in proceedings of Cool Stars 15
conference, St. Andrews, 200
AstraLux - the Calar Alto 2.2-m telescope Lucky Imaging camera
AstraLux is a Lucky Imaging camera for the Calar Alto 2.2-m telescope, based
on an electron-multiplying high speed CCD. By selecting only the best 1-10% of
several thousand short exposure frames, AstraLux provides nearly diffraction
limited imaging capabilities in the SDSS i' and z' filters over a field of view
of 24x24 arcseconds. By choosing commercially available components wherever
possible, the instrument could be built in short time and at comparably low
cost. We briefly present the instrument design, the data reduction pipeline,
and summarise the performance and characteristicsComment: 6 pages, 5 figures, to appear in proceedings of "The Universe under
the Microscope - Astrophysics at High Angular Resolution", published in the
Journal of Physics: Conference Series by Institute of Physics Publishin
Multi-epoch, high spatial resolution observations of multiple T Tauri systems
Context. In multiple pre-main-sequence systems the lifetime of circumstellar
disks appears to be shorter than around single stars, and the actual
dissipation process may depend on the binary parameters of the systems. Aims.
We report high spatial resolution observations of multiple T Tauri systems at
optical and infrared wavelengths. We determine if the components are
gravitationally bound and orbital motion is visible, derive orbital parameters
and investigate possible correlations between the binary parameters and disk
states. Methods. We selected 18 T Tau multiple systems (16 binary and two
triple systems, yielding binary pairs) in the Taurus-Auriga
star forming region from the survey by Leinert et al. (1993), with spectral
types from K1 to M5 and separations from 0.22" (31 AU) to 5.8" (814 AU). We
analysed data acquired in 2006-07 at Calar Alto using the AstraLux lucky
imaging system, along with data from SPHERE and NACO at the VLT, and from the
literature. Results. We found ten pairs to orbit each other, five pairs that
may show orbital motion and five likely common proper motion pairs. We found no
obvious correlation between the stellar parameters and binary configuration.
The 10 m infra-red excess varies between 0.1 and 7.2 magnitudes (similar
to the distribution in single stars, where it is between 1.7 and 9.1), implying
that the presence of the binary star does not greatly influence the emission
from the inner disk. Conclusions. We have detected orbital motion in young T
Tauri systems over a timescale of years. Further observations with
even longer temporal baseline will provide crucial information on the dynamics
of these young stellar systems.Comment: Accepted by A&
Atmosphere-like turbulence generation with surface-etched phase-screens
We built and characterized an optical system that emulates the optical
characteristics of an 8m-class telescope like the Very Large Telescope. The
system contains rotating glass phase-screens to generate realistic
atmosphere-like optical turbulence, as needed for testing multi-conjugate
adaptive optics systems. In this paper we present an investigation of the
statistical properties of two phase-screens etched on glass-plate surfaces,
obtained from Silios Technologies. Those etched screens are highly transmissive
(above 85%) from 0.45 to 2.5 microns. From direct imaging, their Fried
parameter r0 values (0.43+-0.04 mm and 0.81+-0.03 mm, respectively, at 0.633
microns) agree with the expectation to within 10%. This is also confirmed by a
comparison of measured and expected Zernike coefficient variances. Overall, we
find that those screens are quite reproducible, allowing sub-millimetre r0
values, which were difficult to achieve in the past. We conclude that the
telescope emulator and phase-screens form a powerful atmospheric turbulence
generator allowing systematic testing of different kinds of AO instrumentation.Comment: 10 pages, 8 figures, 3 mpeg movies. Submitted to Optics Expres
NGC 346 in The Small Magellanic Cloud. IV. Triggered Star Formation in the HII Region N66
Stellar feedback, expanding HII regions, wind-blown bubbles, and supernovae
are thought to be important triggering mechanisms of star formation. Stellar
associations, being hosts of significant numbers of early-type stars, are the
loci where these mechanisms act. In this part of our photometric study of the
star-forming region NGC346/N66 in the Small Magellanic Cloud, we present
evidence based on previous and recent detailed studies, that it hosts at least
two different events of triggered star formation and we reveal the complexity
of its recent star formation history. In our earlier studies of this region
(Papers I, III) we find that besides the central part of N66, where the bright
OB stellar content of the association NGC346 is concentrated, an arc-like
nebular feature, north of the association, hosts recent star formation. This
feature is characterized by a high concentration of emission-line stars and
Young Stellar Objects, as well as embedded sources seen as IR-emission peaks
that coincide with young compact clusters of low-mass pre-main sequence stars.
All these objects indicate that the northern arc of N66 encompasses the most
current star formation event in the region. We present evidence that this star
formation is the product of a different mechanism than that in the general area
of the association, and that it is triggered by a wind-driven expanding HII
region (or bubble) blown by a massive supernova progenitor, and possibly other
bright stars, a few Myr ago. We propose a scenario according to which this
mechanism triggered star formation away from the bar of N66, while in the bar
of N66 star formation is introduced by the photo-ionizing OB stars of the
association itself.Comment: Astrophysical Journal, In Press. 10 pages, 4 figures, emulateapj
LaTeX style. Figures with Scaled-down resolution. Related Press Releases:
http://www.nasa.gov/mission_pages/spitzer/news/spitzer-20081008.html and
http://www.eso.org/public/outreach/press-rel/pr-2008/pr-34-08.htm