arXiv subjects

M. Altmann

Publications and source records attributed to M. Altmann.

51 records · Page 3Linked to original sources

arXiv2005

3D kinematics of white dwarfs from the SPY project II

We present the kinematics of a sample of 398 DA white dwarfs from the SPY project (ESO SN Ia Progenitor surveY) and discuss kinematic criteria for distinguishing thin-disk, thick-disk, and halo populations. This is the largest homogeneous sample of white dwarfs for which 3D space motions have been determined. Since the percentage of old stars among white dwarfs is higher than among main-sequence stars, they are presumably valuable tools in studies of old populations, such as the halo and the thick disk. Radial velocities and spectroscopic distances were combined with our measurements of proper motions to derive 3D space motions. Galactic orbits were computed. Our kinematic criteria for assigning population membership were deduced from a sample of F and G stars, for which chemical criteria can be used to distinguish between a thin-disk, a thick-disk and a halo star. Our kinematic population classification scheme is based on the position in the U-V-velocity diagram, the position in the Jz-eccentricity diagram, and the Galactic orbit. We combined this with age information and found seven halo and 27 thick-disk white dwarfs in this brightness limited sample. Correspondingly 2% of the white dwarfs belong to the halo and 7% to the thick disk. The mass contribution of the thick-disk white dwarfs is found to be substantial, but is insufficient to account for the missing dark matter. (abbreviated)

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arXiv2005

The Multiwavelength Survey by Yale-Chile (MUSYC): Survey Design and Deep Public UBVRIz' Images and Catalogs of the Extended Hubble Deep Field South

We present UBVRIz' optical images of the 0.32 square degree Extended Hubble Deep Field South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z=3, AGN demographics, and Galactic structure. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62968 objects is complete to a total magnitude of R_AB=25. We select z=3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4/sq. arcmin and an angular correlation function w(theta) = 2.3+-1.0 theta^{-0.8}. (Abridged)

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arXiv2005

High resolution spectroscopy of bright subdwarf B stars - I. Radial velocity variables

Radial velocity curves for 15 bright subdwarf B binary systems have been measured using high precision radial velocity measurements from high S/N optical high-resolution spectra. In addition, two bright sdB stars are discovered to be radial velocity variable but the period could not yet be determined. The companions for all systems are unseen. The periods range from about 0.18 days up to more than ten days. The radial velocity semi amplitudes are found to lie between 15 and 130 km/s. Using the mass functions, the masses of the unseen companions have been constrained to lower limits of 0.03 up to 0.55 M_sun, and most probable values of 0.03 up to 0.81 M_sun. The invisible companions for three of our program stars are undoubtedly white dwarfs. In the other cases they could be either white dwarfs or main sequence stars. For two stars the secondaries could possibly be brown dwarfs. As expected, the orbits are circular for most of the systems. However, for one third of the program stars we find slightly eccentric orbits with small eccentricities of e~0.02-0.06. This is the first time that non-circular orbits have been found in sdB binaries. No correlation with the orbital period can be found.

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arXiv2005

Complete results for five years of GNO solar neutrino observations

We report the complete GNO solar neutrino results for the measuring periods GNO III, GNO II, and GNO I. The result for GNO III (last 15 solar runs) is [54.3 + 9.9 - 9.3 (stat.)+- 2.3 (syst.)] SNU (1 sigma) or [54.3 + 10.2 - 9.6 (incl. syst.)] SNU (1 sigma) with errors combined. The GNO experiment is now terminated after altogether 58 solar exposure runs that were performed between May 20, 1998 and April 9, 2003. The combined result for GNO (I+II+III) is [62.9 + 5.5 - 5.3 (stat.) +- 2.5 (syst.)] SNU (1 sigma) or [62.9 + 6.0 - 5.9] SNU (1 sigma) with errors combined in quadrature. Overall, gallium based solar observations at LNGS (first in GALLEX, later in GNO) lasted from May 14, 1991 through April 9, 2003. The joint result from 123 runs in GNO and GALLEX is [69.3 +- 5.5 (incl. syst.)] SNU (1 sigma). The distribution of the individual run results is consistent with the hypothesis of a neutrino flux that is constant in time. Implications from the data in particle- and astrophysics are reiterated.

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arXiv2004

Kinematics of RHB stars to trace the structure of the galaxy

Red horizontal-branch (RHB) stars have been selected from the HIPPARCOS catalogue to investigate their kinematics and spatial distribution. HIPPARCOS parallaxes, literature radial velocities and HIPPARCOS proper motions, together with models for the gravitational potential of the Milky Way allow a calculation of the actual velocity vectors and the orbits of the RHB stars. The velocity characteristics are used to define a halo population sample (HPS) in the collection of RHBs. The orbits lead statistically to an overall z-distance probability distribution, showing that the RHBs exhibit two populations, a disk one having a scale height of h_disk ~0.6 kpc and a halo one of ~4 kpc. We have investigated the influence on our results of parallax accuracy and of a demarcation line in the HRD between the RHB and the red-giant (RG) star region. Neither of them show marked effects. We have performed the orbit analysis using the potential model of Allen & Santillan as well as of Dehnen & Binney. The results differ only slightly for the disk population, showing that these potential models are not a critical part of such orbit investigations. RHB scale height values are smaller than those found earlier for sdB stars, most likely because the samples of stars used had different spatial distributions a priori. The data do not allow us to specify a trend in the kinematic behaviour of star types along the horizontal branch.

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arXiv2004

Searching for White and Brown Dwarfs in the frame of the MUSYC/CYDER survey

MUSYC (MUltiwavelength Survey by Yale and Chile), and its predecessor, the CYDER (Cal'an Yale Deep Extragalactic Research) survey are both deep multiwavelength surveys mainly aiming at extragalactic issues; however they were both designed with a strong Galactic component in mind. Therefore they consist not only of multipassband imaging (UBVRIzJK) and wide field multi object spectroscopy - it is also foreseen to create a multi-epoch dataset, thus allowing proper motions to be derived using data of 1 and 4-5 years baseline. This enables us to identify fast moving objects, and derive tangential velocities of nearby and intrinsically faint objects, such as White Dwarfs (especially cool WDs) and Brown Dwarfs (BDs). For the former, we will be able to study the faint end of the halo-field luminosity function and determine the fraction of baryonic dark matter consisting of WDs. We will be able to put constraints on the volume density of BDs, and determine whether this density actually meets expectations. Here we give a report of work in progress.

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arXiv2004

3D-Kinematics of White Dwarfs from the SPY-Project

We present kinematics of a sample of 398 DA white dwarfs from the SPY project (ESO SN Ia Progenitor surveY) and discuss kinematic criteria for a distinction of thin disk, thick disk, and halo populations. This is the largest homogeneous sample of white dwarfs for which 3D space motions have been determined. Radial velocities and spectroscopic distances obtained by the SPY project are combined with our measurements of proper motions to derive 3D space motions. Galactic orbits and further kinematic parameters are computed. Our kinematic criteria for assigning population membership are deduced from a sample of F and G stars taken from the literature for which chemical criteria can be used to distinguish between thin disk, thick disk and halo. Our kinematic population classification scheme is based on the position in the U-V-velocity diagram, the position in the J_z-eccentricity diagram and the Galactic orbit. We combine this with age estimates and find seven halo and 23 thick disk white dwarfs.

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arXiv2004

The mass of the sdB primary of the binary HS 2333+3927

Short period sdB binaries with cool companions are crucial to understand pre-CV evolution, because they will evolve into cataclysmic variables, when the sdB will have left the extended horizontal branch. Recently we discovered the sixth such system, HS 2333+3927, consisting of an sdB star and an M dwarf (period: 0.172 d) with a very strong reflection effect, but no eclipses. The reflection is stronger than in any of the other similar systems which renders a quantitative spectral analysis very difficult because the Balmer line profiles may be disturbed by the reflected light. A spectroscopic analysis results in Teff = 36500 K, log g = 5.70, and log (n_He/n_H) = -2.15. Mass-radius relations were derived from the results of the analysis of light and radial-velocity curves. Comparison with the mass-radius relation derived from the surface gravity of the sdB star favours a rather low mass of 0.38 Msun for the primary. The mass of the companion is 0.29 M_sun. HS 2333+3927 is the only known sdB+dM system with a period above the CV period gap.

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arXiv2004

A New 76Ge Double Beta Decay Experiment at LNGS

This Letter of Intent has been submitted to the Scientific Committee of the INFN Laboratori Nazionali del Gran Sasso (LNGS) in March 2004. It describes a novel facility at the LNGS to study the double beta decay of 76Ge using an (optionally active) cryogenic fluid shield. The setup will allow to scrutinize with high significance on a short time scale the current evidence for neutrinoless double beta decay of 76Ge using the existing 76Ge diodes from the previous Heidelberg-Moscow and IGEX experiments. An increase in the lifetime limit can be achieved by adding more enriched detectors, remaining thereby background-free up to a few 100 kg-years of exposure.

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arXiv2003

Studying the populations of our Galaxy using the kinematics of sdB stars

We have analysed the kinematics of a sample of 114 hot subdwarf stars, for 2/3 of which we present new proper motions, spectroscopic and photometric data. The vast majority of the stars show a kinematic behaviour that is similar to that of Thick Disk stars. Some stars have velocities rather fitting to solar, i.e. Thin Disk, kinematics. 16 objects have orbital velocities which differ considerably from those of Disk stars. These are members of the Galactic Halo. We analysed the velocity dispersions and calculated orbits. Most stars feature orbits with disk character (eccentricity <= 0.5), a few reach far above the Galactic plane and have very eccentric orbits (ecc >= 0.7). The intermediate eccentricity range is poorly populated. This indicates that the (Thick) Disk and the Halo are kinematically disjunct. Plotting a histogram of the orbit data points along z leads to the z-distance probability distribution of the star; doing this for all stars leads to the z-distance probability distribution of the sample. The logarithmic histogram shows two slopes, each representing the scale height of a population. The disk component has a scale height of 0.9 (0.1) kpc, which is consistent with earlier results and is similar to that of the Thick Disk. The other slope represents a component with a scale height ~7 kpc, a much flatter gradient than for the disk component. This shows that the vast majority of the sdBs are Disk stars, but a Halo minority is present, too. The kinematic history and population membership of the sdB stars on the whole is different from that of the cooler HBA stars, which are predominantly or even exclusively Halo objects. This leads to the question, whether the Halo sdB stars are of similar origin as the HBAs, or whether their kinematical behaviour possibly represents another origin, such as infalling stellar aggregates.

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arXiv2003

3D kinematics of white dwarfs from the SPY project

We present kinematics of a sample of 107 DA white dwarfs from the SPY project and discuss kinematic criteria for a distinction of thin disk, thick disk, and halo populations. This is the first homogeneous sample of white dwarfs for which 3D space motions have been determined. Studies of white dwarf kinematics can help determine the fraction of the total mass of our Galaxy contained in the form of thick disk and halo white dwarfs. Radial velocities and spectroscopic distances obtained by the SPY project are combined with our measurements of proper motions to derive 3D space motions. Galactic orbits and further kinematic parameters are computed. Candidates for thick disk and halo members are selected in a first step from the classical U-V-velocity diagram. Our final assignment of population membership is based on orbits and position in the angular-momentum-eccentricity diagram. We find four halo and twelve thick disk white dwarfs.

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arXiv2001

Results and plans of the CRESST dark matter search

Data taken by CRESST in 2000 with a cryogenic detector system based on 262 g sapphire crystals is used to place limits on WIMP dark matter in the Galactic Halo. The detector is especially sensitive for low-mass WIMPS with spin-dependent cross sections and improves on existing limits in this region. CRESST is now preparing for a second phase, which will use a 10 kg detector consisting of 300 g CaWO4 crystals with simultaneous detection of phonons and scintillation light to reduce background.

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arXiv2000

GNO Solar Neutrino Observations: Results for GNOI

We report the first GNO solar neutrino results for the measuring period GNOI, solar exposure time May 20, 1998 till January 12, 2000. In the present analysis, counting results for solar runs SR1 - SR19 were used till April 4, 2000. With counting completed for all but the last 3 runs (SR17 - SR19), the GNO I result is [65.8 +10.2 -9.6 (stat.) +3.4 -3.6 (syst.)]SNU (1sigma) or [65.8 + 10.7 -10.2 (incl. syst.)]SNU (1sigma) with errors combined. This may be compared to the result for Gallex(I-IV), which is [77.5 +7.6 -7.8 (incl. syst.)] SNU (1sigma). A combined result from both GNOI and Gallex(I-IV) together is [74.1 + 6.7 -6.8 (incl. syst.)] SNU (1sigma).

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arXiv1998

Proceedings "Neutrino Astrophysics"

Collection of "Extended Abstracts" of talks presented at the SFB-375 workshop NEUTRINO ASTROPHYSICS, Ringberg Castle, Tegernsee, Germany, 20-24 Oct. 1997. Topics include Solar Neutrinos, Supernovae, Gamma-Ray Bursts, High-Energy Neutrinos (atmospheric, astrophysical), Cosmology, and Future Prospects. The focus is on astrophysical and experimental/observational aspects of astrophysical neutrinos while particle theory and neutrino laboratory experiments are not covered.

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arXiv1997

Hot subdwarf stars - galactic orbits and distribution perpendicular to the plane

The spatial distribution and the population nature of subdwarf B type stars in the galaxy is investigated based on the kinematics of these stars. The orbits of 41 stars have been calculated using a galactic mass model. These are well behaved and 10 stars reach to |z| > 2 kpc. Many orbits are very eccentric, reaching in to just 2 kpc from the galactic centre, or veering out to beyond 20 kpc. None of the stars can be identified uniquely as classical Population II objects. The average eccentricity ECC of the orbits of our sample is 0.24, the average normalised z-extent NZE of the orbits is 0.16, and the asymmetric drift of our sample is -36 km s^-1. The distribution in z shows a relative minimum near z=0 pc and has maxima near z=300 pc. This reflects the smaller probability to find the stars IN the disk than away from the disk.

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