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Dive into the research topics where A. Riffeser is active.

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Featured researches published by A. Riffeser.


The Astrophysical Journal | 2001

Detection, photometry and slitless radial velocities of 535 planetary nebulae in the flattened elliptical galaxy ngc 4697

R. H. Mendez; A. Riffeser; R. P. Kudritzki; Michael Matthias; Kenneth C. Freeman; Magda Arnaboldi; M. Capaccioli; Ortwin Gerhard

We have detected 535 planetary nebulae (PNs) in the flattened elliptical galaxy NGC 4697 using the classic on-band, off-band filter technique with the Focal Reducer and Spectrograph at the Cassegrain focus of the first 8 m telescope unit of the ESO Very Large Telescope. From our photometry, we have built the [O III] ?5007 planetary nebula luminosity function (PNLF) of NGC 4697. It indicates a distance of 10.5 ? 1 Mpc to this galaxy, in good agreement with the distance obtained from surface brightness fluctuations and substantially smaller than a previous estimate of 24 Mpc used in earlier dynamical studies. The PNLF also provides an estimate of the specific PN formation rate: (6 ? 2) ? 10-12 PNs yr-1 L?-1. Combining the information from on-band images with PN positions on dispersed, slitless grism images, we have obtained radial velocities for 531 of the 535 PNs. We describe the slitless velocity method and the calibration procedures that we have followed. The radial velocities have errors of about 40 km s-1 and provide kinematic information up to a distance of almost three effective radii from the nucleus. Some rotation is detected in the outer regions, but the rotation curve of this galaxy appears to drop beyond one effective radius. Assuming an isotropic velocity distribution, the velocity dispersion profile is consistent with no dark matter within three effective radii of the nucleus (however, some dark matter can be present if the velocity distribution is anisotropic). We obtain a blue mass-to-light ratio of 11. Earlier M/L ratios for NGC 4697 were too small because of the too large distance used for their derivation.


Astronomy and Astrophysics | 2010

The old and heavy bulge of M 31 - I. Kinematics and stellar populations

R. P. Saglia; Maximilian Fabricius; Ralf Bender; M. Montalto; Chien-Hsiu Lee; A. Riffeser; S. Seitz; L. Morganti; Ortwin Gerhard; Ulrich Hopp

We present new optical long-slit data along 6 position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin from the center, where the disk light contribution is always less than 30%, and out to 8 arcmin along the major axis, where the disk makes 55% of the total light. We show that the velocity dispersions of McElroy (1983) are severely underestimated (by up to 50 km/s). As a consequence, previous dynamical models have underestimated the stellar mass of M31’s bulge by a factor 2. As a further consequence, the light-weighted velocity dispersion of the galaxy grows to 166 km/s and to 170 km/s if also rotation is taken into account, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31 from a factor 3 to a factor 2. The kinematic position angle varies with distance, pointing to triaxiality, but a quantitat ive conclusion can be reached only after simultaneous proper dynamical modeling of the bulge and disk components is performed. We detect gas counterrotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. Using simple stellar population models we derive the age, metallicity and �-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (�12 Gyr, with many best-fit ages at the model grid limit of 15 Gyr), slightly �-elements overabundant ([�/Fe]�0.2) and at solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match reasonably well the dust-corrected observ ations, within the known limitations of current simple stellar population models. The stellar populations have approximately radially constant mass(“)


Astronomy and Astrophysics | 2007

X-ray monitoring of optical novae in M 31 from July 2004 to February 2005

W. Pietsch; F. Haberl; G. Sala; Holger Stiele; K. Hornoch; A. Riffeser; J. Fliri; Ralf Bender; S. Bühler; Vadim Burwitz; J. Greiner; S. Seitz

Context. Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra  observations. Aims. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra  HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. Methods. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. Results. For comparison with the X-ray data we created a catalogue of optical novae in M 31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380 d after outburst. One nova is detected to turn on 50 d, another 200 d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. Conclusions. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>


Astronomy and Astrophysics | 2005

Optical novae: the major class of supersoft X-ray sources in M 31

W. Pietsch; J. Fliri; Michael J. Freyberg; J. Greiner; F. Haberl; A. Riffeser; G. Sala

30\%


The Astrophysical Journal | 2008

The carbon-rich type Ic SN 2007gr: the photospheric phase

S. Valenti; N. Elias-Rosa; S. Taubenberger; V. Stanishev; I. Agnoletto; Daniel N. Sauer; E. Cappellaro; Andrea Pastorello; Stefano Benetti; A. Riffeser; Ulrich Hopp; H. Navasardyan; D.Y. Tsvetkov; V. Lorenzi; Ferdinando Patat; Massimo Turatto; R. Barbon; Stefano Ciroi; F. Di Mille; S. Frandsen; J. P. U. Fynbo; Peter Laursen; Paolo A. Mazzali

). We use the X-ray light curves to estimate the burned masses of the White Dwarf and of the ejecta.


Monthly Notices of the Royal Astronomical Society | 2014

Weak lensing analysis of SZ-selected clusters of galaxies from the SPT and Planck surveys

D. Gruen; S. Seitz; Fabrice Brimioulle; R. Kosyra; J. Koppenhoefer; Chien-Hsiu Lee; Ralf Bender; A. Riffeser; T. Eichner; T. Weidinger; M. Bierschenk

We searched for X-ray counterparts of optical novae detected in M 31 and M 33. We combined an optical nova catalogue from the WeCAPP survey with optical novae reported in the literature and correlated them with the most recent X-ray catalogues from ROSAT, XMM-Newton, and Chandra, and – in addition – searched for nova correlations in archival data. We report 21 X-ray counterparts for novae in M 31 – mostly identified as supersoft sources (SSS) by their hardness ratios – and two in M 33. Our sample more than triples the number of known optical novae with a supersoft X-ray phase. Most of the counterparts are covered in several observations allowing us to constrain their X-ray light curves. Selected brighter sources were classified by their XMM-Newton EPIC spectra. We use the well-determined start time of the SSS state ( �� ) ( �� ) ( �� )


Astronomy and Astrophysics | 2002

Image reduction pipeline for the detection of variable sources in highly crowded fields

C. A. Gössl; A. Riffeser

The first 2 months of spectroscopic and photometric monitoring of the nearby Type Ic SN 2007gr are presented. The very early discovery (less than 5 days after the explosion) and the relatively short distance of the host galaxy motivated an extensive observational campaign. SN 2007gr shows an average peak luminosity but unusually narrow spectral lines and an almost flat photospheric velocity profile. The detection of prominent carbon features in the spectra is shown and suggests a wide range in carbon abundance in stripped-envelope supernovae. SN 2007gr may be an important piece in the puzzle of the observed diversity of CC SNe.


The Astrophysical Journal | 2003

The Wendelstein Calar Alto Pixellensing Project* (WeCAPP): First MACHO Candidates

A. Riffeser; Jürgen Fliri; Ralf Bender; S. Seitz; Claus Gössl

We present the weak lensing analysis of the Wide-Field Imager SZ Cluster of Galaxy (WISCy) sample, a set of ten clusters of galaxies selected for their Sunyaev-Zel’dovich (SZ) effect. After developing new and improved methods for background selection and determination of geometric lensing scaling factors from absolute multi-band photometry in cluster fields, we compare the weak lensing result with public X-ray and SZ data. We find consistency with published hydrostatic X-ray masses with no significant bias and an intrinsic scatter σint,log10 = 0.13 +0.11 0.13 . We independently calibrate the SPT significance-mass relation and find consistency with previous results at an intrinsic scatter of σint,log10 = 0.09 +0.15 0.09 , with indications for a slightly higher normalisation mass and steeper slope. The comparison of weak lensing mass and Planck Compton parameters, whether extracted self-consistently with a mass-observable relation (MOR) or using X-ray prior information on cluster size, shows significant discrepancies. Since the deviations from the MOR strongly correlate with cluster redshift, we hypothesise that they are related to a size or redshift dependent bias in either signal extraction in the Planck SZ catalogues or their previous X-ray based mass calibration, or in measurement related excess intrinsic scatter.


The Astrophysical Journal | 2005

Planetary Nebulae and Stellar Kinematics in the Flattened Elliptical Galaxy NGC 1344

A. M. Teodorescu; R. H. Mendez; R. P. Saglia; A. Riffeser; R. P. Kudritzki; Ortwin Gerhard; Jan Kleyna

We present a reduction pipeline for CCD (charge-coupled device) images which was built to search for variable sources in highly crowded fields like the M31 bulge and to handle extensive databases due to large time series. We describe all steps of the standard reduction in detail with emphasis on the realisation of per pixel error propagation: Bias correction, treatment of bad pixels, flatfielding, and filtering of cosmic rays. The problems of conservation of PSF (point spread function) and error propagation in our image alignment procedure as well as the detection algorithm for variable sources are discussed: We build difference images via image convolution with a technique called OIS (optimal image subtraction, Alard & Lupton, 1998), proceed with an automatic detection of variable sources in noise dominated images and finally apply a PSF-fitting, relative photometry to the sources found. For the WeCAPP project (Riffeser et al., 2001) we achieve 3� detections for variable sources with an apparent brightness of e.g. m = 24.9 mag at their minimum and a variation ofm = 2.4 mag (or m = 21.9 mag brightness minimum and a variation ofm = 0.6 mag) on a background signal of 18.1 mag/arcsec 2 based on a 500 s exposure with 1.5 arcsec seeing at a 1.2 m telescope. The complete per pixel error propagation allows us to give accurate errors for each measurement.


Monthly Notices of the Royal Astronomical Society | 2013

Weak lensing analysis of RXC J2248.7−4431

D. Gruen; Fabrice Brimioulle; S. Seitz; Chien-Hsiu Lee; J. Young; J. Koppenhoefer; T. Eichner; A. Riffeser; V. Vikram; T. Weidinger; A. Zenteno

We report the detection of the first two microlensing candidates from the Wendelstein Calar Alto Pixellensing Project (WeCAPP). Both are detected with a high signal-to-noise ratio and were filtered out from 4.5 million pixel light curves using a variety of selection criteria. Here we only consider well-sampled events with timescales of 1 day < tfwhm < 20 days, high amplitudes, and a low χ2 of the microlensing fit. The two-color photometry (R, I) shows that the events are achromatic and that giant stars with colors of (R-I) ≈ 1.1 mag in the bulge of M31 have been lensed. The magnification factors are 64 and 10, which are obtained for typical giant luminosities of MI = -2.5 mag. Both lensing events lasted for only a few days (t = 1.7 days and t = 5.4 days). The event GL1 is likely identical with PA-00-S3 reported by the POINT-AGAPE project. Our calculations favor in both cases the possibility that MACHOs in the halo of M31 caused the lensing events. The most probable masses, 0.08 M☉ for GL1 and 0.02 M☉ for GL2, are in the range of the brown dwarf limit of hydrogen burning. Solar mass objects are a factor of 2 less likely.

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