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S. Schuh

Publications and source records attributed to S. Schuh.

36 records · Page 2Linked to original sources
arXiv2007

A new period determination for the close PG1159 binary SDSSJ212531.92-010745.9

Methods to measure masses of PG1159 stars in order to test evolutionary scenarios are currently based on spectroscopic masses or asteroseismological mass determinations. One recently discovered PG1159 star in a close binary system may finally allow the first dynamical mass determination, which has so far been analysed on the basis of one SDSS spectrum and photometric monitoring. In order to be able to phase future radial velocity measurements of the system SDSSJ212531.92-010745.9, we follow up on the photometric monitoring of this system to provide a solid observational basis for an improved orbital ephemeris determination. New white-light time series of the brightness variation of SDSSJ212531.92-010745.9 with the Tuebingen 80cm and Goettingen 50cm telescopes extend the monitoring into a second season (2006), tripling the length of overall observational data available, and significantly increasing the time base covered. We give the ephemeris for the orbital motion of the system, based on a sine fit which now results in a period of 6.95573(5)h, and discuss the associated new amplitude determination in the context of the phased light curve variation profile. The accuracy of the ephemeris has been improved by more than one order of magnitude compared to that previously published for 2005 alone.

astro-ph↗
arXiv2007

Light curve analysis of the hybrid sdB pulsators HS0702+6043 and HS2201+2610

We present the detection of low-amplitude, long-period g-modes in two individual sdBV stars which are known to be p-mode pulsators. Only few of these hybrid objects, showing both p- and g-modes, are known today. We resolve the g-mode domain in HS0702+6043 and add HS2201+2610 to the list of hybrid pulsators. To discover the low-amplitude g-modes, a filtering algorithm based on wavelet transformations was applied to denoise observational data.

astro-ph↗
arXiv2007

The MSST Campaign: II.Effective temperature and gravity variations in the multi-periodic pulsating subdwarf B star PG1605+072

Stellar oscillations are an important tool to probe the interior of a star. Subdwarf B stars are core helium burning objects, but their formation is poorly understood as neither single star nor binary evolution can fully explain their observed properties. Since 1997 an increasing number of sdB stars has been found to pulsate forming two classes of stars (the V361 Hya and V1093 Her stars). We focus on the bright V 361 Hya star PG1605+072 to characterize its frequency spectrum. While most previous studies relied on light variations, we have measured radial velocity variations for as much as 20 modes. In this paper we aim at characterizing the modes from atmospheric parameter and radial velocity variations. Time resolved spectroscopy ($\approx$9000 spectra) has been carried out to detect line profile variations from which variations of the effective temperature and gravity are extracted by means of a quantitative spectral analysis. We measured variations of effective temperatures and gravities for eight modes with semi-amplitudes ranging from $ΔT_{\rm{eff}}=880$ K to as small as 88 K and $Δ\log{g}$ of 0.08 dex to as low as 0.008 dex. Gravity and temperature vary almost in phase, whereas phase lags are found between temperature and radial velocity. This profound analysis of a unique data set serves as sound basis for the next step towards an identification of pulsation modes. As rotation may play an important role the modelling of pulsation modes is challenging but feasible.

astro-ph↗
arXiv2007

The O-C diagram of the subdwarf B pulsating star HS2201+2610: detection of a giant planet?

In this article we present the O-C diagram of the hot subdwarf B pulsating star HS2201+2610 after seven years of observations. A secular increase of the main pulsation period, Pdot=(1.3+-0.1)x10**(-12), is inferred from the data. Moreover, a further sinusoidal pattern suggests the presence of a low-mass companion (Msini=~3.5 Mjup), orbiting the hot star at a distance of about 1.7 AU with a period near 1140 days.

astro-ph↗
arXiv2007

Spectral types of planetary host star candidates from OGLE III

The Optical Gravitational Lensing Experiment project has recently provided the OGLE III list of low-luminosity object transits from campaigns #3 and #4, reporting 40 new objects exhibiting the low-amplitude photometric eclipses expected for exoplanets. Compared to previous OGLE targets, these OGLE III candidates have been more restrictively selected and may contain low-mass planets. We have secured follow-up low-resolution spectroscopy for 28 candidates out of this list (and one from the OGLE Carina fields) to obtain an independent characterization of the primary stars by spectral classification and thus better constrain the parameters of their companions. We fed the constraints from these results back into an improved light curve solution. Together with the radius ratios from the transit measurements, we derived the radii of the low-luminosity companions. This allows us to examine the possible sub-stellar nature of these objects. Sixteen of the companions can be clearly identified as low-mass stars orbiting a main sequence primary, while 10 more objects are likely to have red giant primaries and therefore also host a stellar companion; 3 possibly have a sub-stellar nature R< 0.15 R_sun). The planetary nature of these objects should therefore be confirmed by dynamical mass determinations.

astro-ph↗
arXiv2006

The first PG1159 close binary system

The archival spectrum of SDSS J212531.92-010745.9 shows not only the typical signature of a PG1159 star, but also indicates the presence of a companion. With time-series photometry of SDSS J212531.92-010745.9 during 10 nights, spread over one month, with the T"ubingen 80cm and the G"ottingen 50cm telescopes, the binary nature of this object has recently been proven. An orbital period of 6.9h could be determined, and the observed light curve fitted with the nightfall program. A comparison of the spectrum of SDSS J212531.92-010745.9 with NLTE models further constrained the light curve solution. We emphasize that this is the first system of this kind which will allow a dynamical mass determination for a PG1159 star.

astro-ph↗
arXiv2006

Soft X-ray Spectroscopy of the Hot DA White Dwarf LB1919 and the PG1159 Star PG1520+525

We have performed soft X-ray spectroscopy of two hot white dwarfs with the Chandra observatory using the Low Energy Transmission Grating. The first target is the hot DA white dwarf LB1919 (Teff=69000 K). This star is representative of a small group of hot DAs whose metallicities lie well below predictions from radiative levitation theory. The Chandra spectrum shows a rich absorption line spectrum which may allow to find the origin of the low-metallicity nature of these DAs. The second target is PG1520+525, a very hot non-pulsating PG1159 star. We find that it is hotter (Teff=150 000 K) than the pulsating prototype PG1159-035 (Teff=140 000) and conclude that both stars confine the blue edge of the GW Vir instability strip.

astro-ph↗
arXiv2006

SDSSJ212531.92-010745.9 - the first definite PG1159 close binary system

The archival spectrum of SDSSJ212531.92-010745.9 shows not only the typical signature of a PG1159 star, but also indicates the presence of a companion. Our aim was the proof of the binary nature ofthis object and the determination of its orbital period.We performed time-series photometry of SDSSJ212531.92-010745.9. We observed the object during 10 nights, spread over one month, with the Tuebingen 80cm and the Goettingen 50cm telescopes. We fitted the observed light curve with a sine and simulated the light curve of this system with the nightfall program. Furthermore, we compared the spectrum of SDSSJ212531.92-010745.9 with NLTE models, the results of which also constrain the light curve solution. An orbital period of 6.95616(33)h with an amplitude of 0.354(3)mag is derived from our observations. A pulsation period could not be detected. For the PG1159 star we found, as preliminary results from comparison with our NLTE models, Teff about 90000K, log g about 7.60, and the abundance ratio C/He = 0.05 by number fraction. For the companion we obtained with a mean radius of 0.4 +/- 0.1 Rsol, a mass of 0.4 +/- 0.1 Msol, and a temperature of 8200K on the irradiated side, good agreement between the observed light curve and the nightfall simulation, but we do not regard those values as final.

astro-ph↗
arXiv2005

Exciting new features in the frequency spectrum of the EC14026 star HS0702+6043 - Simultaneous g-modes and p-modes in a sdB pulsator

The discovery of a long-period g-mode oscillation in the previously known short-period p-mode sdB pulsator HS0702+6043 makes this star an extraordinary object, unique as a member of the family of sdB pulsators, and one of the very few known pulsating stars overall exhibiting excited modes along both the acoustic and gravity branches of the nonradial pulsation spectrum. Because p-modes and g-modes probe different regions of a pulsating star, HS0702+6043 holds a tremendous potential for asteroseismological investigations. We present preliminary results from the first extended campaign on this object.

astro-ph↗
arXiv2005

HS0702+6043: A star showing both short-period p-mode and long-period g-mode oscillations

[Context.] The hot subdwarf B star HS0702+6043 is known as a large-amplitude, short-period p-mode pulsator of the EC14026 type. Its atmospheric parameters place it at the common boundary between the empirical instability regions of the EC14026 variables and the typically cooler long-period g-mode pulsators of the PG1716 kind. [Aims.] We analyse and interpret the photometric variability of HS0702+6043 in order to explore its asteroseismological potential. [Methods.] We report on rapid wide band CCD photometric observations to follow up on and confirm the serendipitous discovery of multiperiodic long-period luminosity variations with typical time scales of ~1h in HS0702+6043, in addition to the two previously known pulsations at 363s and 383s. In particular, we isolate a relatively low-amplitude (~4 mmag), long-period (3538+-130s) light variation. [Results.] We argue that the most likely origin for this luminosity variation is the presence of an excited g-mode pulsation. If confirmed, HS0702+6043 would constitute a rare addition to the very select class of pulsating stars showing simultaneously parts of their pressure and gravity mode pulsation spectra. The asteroseismological potential of such stars is immense, and HS0702+6043 thus becomes a target of choice for future investigations. While our discovery appears consistent with the location of HS0702+6043 at the common boundary between the two families of pulsating sdB stars, it does challenge theory's current description of stability and driving mechanisms in pulsating B subdwarfs.

astro-ph↗
arXiv2005

The Cleo Rich Detector

We describe the design, construction and performance of a Ring Imaging Cherenkov Detector (RICH) constructed to identify charged particles in the CLEO experiment. Cherenkov radiation occurs in LiF crystals, both planar and ones with a novel ``sawtooth''-shaped exit surface. Photons in the wavelength interval 135--165 nm are detected using multi-wire chambers filled with a mixture of methane gas and triethylamine vapor. Excellent pion/kaon separation is demonstrated.

physics.ins-det↗
arXiv2004

Discovery of a Long-Period Photometric Variation in the V361 Hya Star HS 0702+6043

We report the discovery of a long-period g-mode oscillation in the previously known short-period p-mode sdB pulsator HS 0702+6043. This makes this star an extraordinary object, unique as a member of the family of sdB pulsators, and one of the very few known pulsating stars overall exhibiting excited modes along both the acoustic and gravity branches of the nonradial pulsation spectrum. Because p-modes and g-modes probe different regions of a pulsating star, HS 0702+6043 holds a tremendous potential for future detailed asteroseismological investigations.

astro-ph↗
arXiv2004

Metal Abundances in Hot DA White Dwarfs

We compare measured element abundances in hot DA white dwarfs from UV observations to predictions from our self-consistent non-LTE model atmosphere diffusion calculations.

astro-ph↗
arXiv2000

The Cleo III Ring Imaging Cherenkov Detector

The CLEO detector has been upgraded to include a state of the art particle identification system, based on the Ring Imaging Cherenkov Detector (RICH) technology, in order to take data at the upgraded CESR electron positron collider. The expected performance is reviewed, as well as the preliminary results from an engineering run during the first few months of operation of the CLEO III detector.

hep-ex↗
arXiv1999

Performance of the CLEO III LiF-TEA Ring Imaging Cherenkov Detector in a High Energy Muon Beam

The CLEO III Ring Imaging Cherenkov detector uses LiF radiators to generate Cherenkov photons which are then detected by proportional wire chambers using a mixture of CH$_4$ and TEA gases. The first two photon detector modules which were constructed, were taken to Fermilab and tested in a beam dump that provided high momentum muons. We report on results using both plane and "sawtooth" shaped radiators. Specifically, we discuss the number of photoelectrons observed per ring and the angular resolution. The particle separation ability is shown to be sufficient for the physics of CLEO III.

hep-ex↗
arXiv1999

The CLEO-III RICH Detector and Beam Test Results

We are constructing a Ring Imaging Cherenkov detector (RICH) for the CLEO III upgrade for precision charged hadron identification. The RICH uses plane and sawtooth LiF crystals as radiators, MWPCs as photon detectors with TEA as the photo-sensitive material, and low-noise Viking readout electronics. Results of a beam test of the first two out of total 30 sectors are presented.

hep-ex↗
arXiv1999

The CLEO-III Ring Imaging Cherenkov Detector

The CLEO-III Detector upgrade for charged particle identification is discussed. The RICH design uses solid LiF crystal radiators coupled with multi-wire chamber photon detectors, using TEA as the photosensor, and low-noise Viking readout electronics. Results from our beam test at Fermilab are presented.

hep-ex↗