86,631 research outputs found
The MONET project and beyond
No full textThe "MOnitoring NEtwork of Telescopes" (MONET) consists of two 1.2-m imaging telescopes funded by the Alfried Krupp von Bohlen und Halbach Foundation and the Georg-August-Universitat Gottingen and will be operated by the McDonald Observatory in West Texas and the South African Astronomical Observatory at Sutherland. Scheduled to go into full operation in 2005, it will be used to perform a variety of monitoring and survey observations over the whole sky, to aid observations by satellites and 10m-class telescopes like the VLT, HET and SALT telescopes, and will be available to participating school classes all over the world. Through our development and use of Remote Telescope Markup Language (RTML), MONET should be one of the kernels of a growing international network of heterogeneous telescopes
The difficulty of measuring the local dark matter density
No full textThe analysis of the vertical velocity dispersion of disc stars in the local Milky Way is the most direct astronomical means of estimating the local dark matter density, ρDM. Current estimates for ρDM based on the mid-plane dynamic density use a local baryonic correction that ignores the non-local effects of spiral structure and significantly underestimates the amount of dynamically relevant gas now known to be present in the ISM; the additional gas plus the remaining uncertainties make it practically impossible to measure ρDM from mid-plane kinematics alone. The sampling of inhomogeneous tracer populations with different scale-heights and scale-lengths results in a systematic increase in the observed dispersion gradients and changes in the nominal density distributions that, if not properly considered, can be misinterpreted as a sign of more dark matter. If the disc gravity is modelled locally using an infinite disc, the local variation in the vertical gravity due to the globally exponential disc components results in an underestimation of the baryonic contribution by as much as ~40%. Given only the assumptions of stationarity, an axially and vertically symmetric disc, doubly exponential tracer and mass-component density profiles, a phenomenologically justified model for the cross-dispersion component σRz, and a realistic model for gz(z), it is possible to solve the full vertical Jeans equation analytically for the vertical dispersion σz(z) and hence test the robustness of previous attempts at measuring ρDM. When the model parameters for σRz are estimated from SEGUE G dwarf star data, it is still not possible to explain the difference in behaviour seen in the simple thick- and thin-disc datasets reported by Buedenbender et al. (2014, MNRAS, submitted). Rather than being a fundamental problem with the kinematical model, this effect appears to be a further sign of the difficulty of defining and handling kinematically homogeneous tracer populations
USING OPEN SOURCE SOFTWARE AND OPEN STANDARDS FOR OPERATING ROBOTIC TELESCOPES
No full textThe University of G¨ottingen, the McDonald Observatory of the University of Texas at Austin, and the South African Astronomical Observatory (SAAO) operate two robotic telescopes called MONET at McDonald Observatory in Fort Davis, Texas (MONET/North), and at the SAAO in Sutherland, South Africa (MONET/South). After problems with our original observation control system and some difficulties with another one, we decided to build our own system, initially providing only the minimally required functionality, but allowing for easy extensibility. A decision was made to build on open standards and open source software only, so that we can use existing and well-tested technologies. In this paper we will describe our efforts to implement such an open observation control system using HTTP and XMPP. Furthermore, we will discuss possibilities for connecting multiple telescopes via VOEvents and RTML
The Bosma effect revisited
No full textContext. The observed proportionality between the centripetal
contribution of the dynamically insignificant HI gas in the discs of spiral galaxies and
the dominant contribution of dark matter (DM) – the “Bosma effect” – has been repeatedly
mentioned in the literature but largely ignored. Since this phenomenology, if
statistically significant, tells us something about the relationship between the visible
baryonic and invisible DM, it is important to re-examine the reality of this effect using
formal tests and more modern data.
Aims. We have re-examined the evidence for the Bosma effect, either by
scaling the contribution of the HI gas alone or by using both the observed stellar disc
and HI gas as proxies.
Methods. We have calculated Bosma effect models for 17 galaxies in The
HI Nearby Galaxy Survey data set. The results are compared with two models for exotic cold
DM: internally consistent cosmological Navarro-Frenk-White (NFW) models with constrained
compactness parameters, and “universal rotation curve” (URC) models using fully
unconstrained Burkert density profiles.
Results. Fits to spiral galaxy rotation curves computed using just HI
scaling are inadequate, despite the clear proportionality seen in the outer discs. The
poor performance is obviously related to the prominent decrease in the HI surface density
in regions of high stellar surface density, where HI has been converted into molecules and
stars. The Bosma models that partially correct for this physical effect using the stellar
discs as additional proxies are statistically nearly as good as the URC models and clearly
better than the NFW ones.
Conclusions. We confirm the correlation between the centripetal effects
of DM and that of the interstellar medium of spiral galaxies. The efficacy of “maximal
disc” models is explained as the natural consequence of “classic” Bosma models which
include the stellar disc as a proxy in regions of reduced atomic gas. The perception that
the Bosma effect could be due to the near-equality of the HI surface density and the
projected mass density of a cold DM halo is incorrect, both theoretically and empirically.
The standard explanation – that the effect reflects a statistical correlation between the
visible and exotic DM – seems highly unlikely, given that the geometric forms and hence
centripetal signatures of spherical halo and disc components are so different. A literal
interpretation of the Bosma effect as being due to the presence of significant amounts of
disc DM requires a median visible baryon to disc DM ratio of about 40%
Detecting circumstellar disks around gravitational microlenses
No full textAims. We investigate the chance of detecting proto-planetary or debris disks in
stars that induce microlensing event (lenses), and consider the modification
of the light curve shapes due to occultation and extinction by the disks,
as well as the gravitational deflection caused by the additional mass.
Methods. The magnification of gravitational microlensing events is calculated using the ray shooting method. The occultation is taken into account by neglecting or weighting the images on the lens plane according to a transmission map of the corresponding disk for a point source point lens (PSPL) model. The estimated frequency of events is obtained by considering the possible inclinations and optical depths of the disk.
Results. We conclude that gravitational microlensing can be used, in principle, as a
tool for detecting debris disks beyond 1 kpc, but estimate that each year around 1 debris disk is expected for lens stars of F, G, or K spectral type and about 10 debris disks might have shown signatures in existing datasets
Robotic Astronomy – Proceedings of the 3rd Potsdam Thinkshop on Robotic Astronomy
No full textFrom July 12-15, 2004, the third Potsdam Thinkshop was held in the Hotel Dorint "Sanssouci" in Potsdam, Germany on the topic of ROBOTIC ASTRONOMY. Its aim was to bring together astronomers and technicians from any field in astronomy to review the current status of robotic telescope projects and to discuss the future science cases for such installations. Part of the "Thinkshop" concept of this meeting was to jointly think about new scientific projects tailored to the unique capabilities of modem robotic telescopes, small and large
The quest for companions to post-common envelope binaries
No full textWe present 69 new mid-eclipse times of the young post-common envelope binary (PCEB) NN Se
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