arXiv subjects

C. Tappert

Publications and source records attributed to C. Tappert.

At least 55 records · Page 3Linked to original sources

arXiv2008

RR Pictoris: an old nova showing superhumps and QPOs

We present time-resolved V-photometry of the old nova RR Pic. Apart from the hump-like variability, the light curves show the strong flickering and random variation typical for RR Pic. We do not find any convincing evidence for the previously reported eclipse. The extrapolated eclipse phase coincides with a broad minimum, but comparing the overall shape of the light curve suggests that the eclipse should actually be located around phase 0.2. The orbital period which we derive from these data agrees well with the old one, any uncertainty is too small to account for the possible phase shift. Apart from the 3.48h period, which is usually interpreted as the orbital one, we find an additional period at P=3.78h, which we interpret as the superhump period of the system; the corresponding precession period at 1.79d is also present in the data. We also find indications for the presence of a 13min quasi-periodic oscillation.

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arXiv2008

NSV 13983: A New Dwarf Nova in the Period Gap

Aims. NSV 13983 is catalogued as a dwarf nova based on a reported outburst from 2005. The system has not yet been studied spectroscopically. We attempt to confirm its nature as a dwarf nova and determine its orbital period. Methods. We derive the orbital period by using time-resolved spectroscopic data to measure radial velocities. Results. The average spectrum shows evidence that the system is a dwarf nova in quiescence. The radial velocity curves derived from measurements of the spectral lines Hαand Hβ, show a clear modulation with a period of 2.76 h. This places NSV 13983 below the upper edge of the gap in the period distribution of cataclysmic variables, implying that it is the 14th dwarf nova in the gap.

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arXiv2007

The remarkable properties of the symbiotic star AE Circinus

We present new optical spectroscopy and photometry, 2MASS infrared observations and 24 years of combined AAVSO and AFOEV photometry of the symbiotic star candidate æ. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of $\sim 2 \times 10^{-4}$ mag/day. The whole range of variability of the star in the $V$ band is about 4 magnitudes. The periodogram of the photometric data reveals strong signals at $\sim$ 342 and 171 days. The presence of the emission feature at $λ$ 6830 Åat minimum and the detection of absorption lines of a $\sim$ K5 type star confirm the symbiotic classification and suggest that AE Cir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the $λ$ 6830 Åemission feature and the weakness of the He II 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission line flickering in time scales of minutes in 2001. The peculiar character of æis revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts.

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arXiv2007

The pre-cataclysmic variable, LTT560

System parameters of the object LTT560 are determined in order to clarify its nature and evolutionary status. We apply time-series photometry to reveal orbital modulations of the light curve, time-series spectroscopy to measure radial velocities of features from both the primary and the secondary star, and flux-calibrated spectroscopy to derive temperatures of both components. We find that LTT560 is composed of a low temperature T~7500K DA white dwarf as the primary and an M5.5+-1 main-sequence star as the secondary component. The current orbital period is Porb=3.54(07)h. We derive a mass ratio Msec/Mwd = 0.36(03) and estimate the distance to d=25-40pc. Long-term variation of the orbital light curve and an additional H-alpha emission component on the white dwarf indicate activity in the system, probably in the form of flaring and/or accretion events.

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arXiv2007

K-band spectroscopy of pre-cataclysmic variables

We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12CO and 13CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs. All our systems show CO abundances that are within the range observed for single stars. The weakest 12CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs.

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arXiv2006

The emission line galaxy TV Reticuli: Evidence for an ultraluminous supernova

TV Ret was classified as a cataclysmic variable due to an outburst observed in 1977. We intended to confirm this classification and derive some basic properties of the system. Low resolution optical spectra were obtained for a spectral classification of the object. We find that the object is not a cataclysmic variable but an emission line galaxy with a redshift z=0.0964. An R-image taken in very good seeing conditions shows that the object is extended. We show that TV Ret is a blue dwarf galaxy, probably compact, with an absolute magnitude of MB = -17.5, a metallicity of 0.12 solar, and an average temperature of 1.3 10^4 K. The line ratios place it among the HII galaxies, although close to the border of the Seyfert2s. The outburst, which was observed in 1977, could thus be explained by a supernova explosion. However, with an absolute magnitude around MB = -21, it was an extremely bright one.

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arXiv2006

AD Mensae: a dwarf nova in the period gap

AD Men was classified as a probable long-period dwarf nova based on its long-term variability. Recent spectroscopic data instead suggested a short-period system. With the here presented observations we aim at clarifying its nature. Time--resolved photometry and spectroscopy has been used to get information on the orbital period of this system. The light curve shows the typical flickering and a clear hump--like periodic modulation with an average amplitude of 0.3mag and a period of P=2.20(02)h. The radial velocity measurements of the Halpha emission line confirm this value as the orbital period. AD Men is thus located at the lower end of, but clearly inside, the gap of the period distribution of cataclysmic variables, making it one of only 11 dwarf novae in this important period range.

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arXiv2006

Spectroscopy of the candidate pre-CV LTT 560

We present preliminary results on spectroscopic data of the candidate pre-cataclysmic variable LTT 560. A fit to the flux-calibrated spectrum reveals the temperature of the white-dwarf primary to be T_eff = 7000 - 7500 K, and confirms the result of previous studies on the detection of an M5V secondary star. The analysis of radial velocity data from spectral features attributed to the primary and the secondary star shows evidence for low-level accretion.

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arXiv2005

Spectroscopic classification of cataclysmic variable candidates

We present low resolution optical spectroscopy for six cataclysmic variable candidates and the old nova V888 Cen. We confirm the classification as cataclysmic variable for LB 9963 and FQ Mon, while the other four candidates turn out to be different type of stars. We discuss the individual spectra and pay special attention to the mass transfer rate and disc temperature and density of the three cataclysmic variables.

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arXiv2004

Spectroscopic analysis of tremendous--outburst--nova candidates

In the course of a long-term project investigating classical novae with large outburst amplitudes, we have performed optical spectroscopy of several old-nova candidates. We here present the spectra of the candidates V630 Sgr, XX Tau, CQ Vel, V842 Cen, and V529 Ori, that hitherto lacked such classification. While the first four show typical spectra for cataclysmic variables, and can thus be identified as such, V529 Ori is probably misclassified. Of special interest are the two systems XX Tau and V842 Cen, which show all signs for being low mass transfer systems. As such they can be used to judge the evolution scenarios for novae. In particular, given the rather young age of their outburst, it appears more likely that these systems are not on their way into hibernation, (i.e., cutting off mass transfer for a longer period of time), but are simply settling down towards their original configuration of comparatively low, but steady, mass transfer, such as for dwarf novae.

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arXiv2004

IR spectroscopy of pre-cataclysmic binaries

We have taken near-infrared (JHK) spectroscopic data of a sample of pre-CVs, in order to examine them for signatures of nuclear evolution. Here we present preliminary results for the three systems BPM 71214, RR Cae, and RE 1016-053.

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arXiv2004

Cataclysmic variables from the Calan-Tololo-Survey -- I. Photometric periods

In a search for cataclysmic variables in the Calan-Tololo Survey we have detected 21 systems, 16 of them previously unknown. In this paper we present detailed time-series photometry for those six confirmed cataclysmic variables that show periodic variability in their light curves. Four of them turned out to be eclipsing systems, while the remaining two show a modulation consisting of two humps. All derived periods are below, or, in one case, just at the lower edge of the period gap.

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arXiv2003

Search for brown-dwarf like secondaries in cataclysmic variables II

We have examined VTL/ISAAC 1-2.5 $\umu$m spectroscopy of a sample of short orbital period cataclysmic variables which are candidates for harboring substellar companions. We provide descriptions of the infrared spectrum of \hbox{EI Psc}, \hbox{V834 Cen}, \hbox{WX Cet}, \hbox{VW Hyi}, \hbox{TY PsA} and \hbox{BW Scl}. Fitting of the IR spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. Absorption features of the secondary star were detected in \hbox{EI Psc} and \hbox{V834 Cen}, consistent with dwarf secondaries of spectral type K 5 $\pm$ 1 and M 8 $\pm$ 0.5, respectively. In addition, we report the first detection of the secondary star in \hbox{VW Hyi}. The SED in this case is well matched by an L 0 $\pm$ 2 type secondary contributing 23 per cent to the overall flux at $λ$ = 1.15 $\umu$m. This is a surprising result for a system with a relatively high mass transfer rate. We discuss the implication of our findings on the current scenarios for cataclysmic variable star evolution.

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arXiv2003

Recovery of the old nova V840 Ophiuchi: A carbon rich system

We present optical spectroscopy and multi colour photometry of the old nova V840 Oph. We rediscovered the nova based on its position in the colour--colour diagrams. It stands out as a very blue object with an additional red component. We present the first optical spectroscopy of this candidate and confirm its nova character. Furthermore, V840\,Oph has been found as one of very few cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the analysis of the carbon lines it seems probable that V840 Oph contains actually a carbon-rich secondary star. So far, only the nova-like QU Car has been known to have such a companion. We furthermore find spectroscopic evidence that V840 Oph has a hot, dense accretion disc or stream and is probably a magnetic system.

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arXiv2003

An atlas of line profile studies for SU UMa type cataclysmic variables

We present H-alpha line-profile analyses for the seven SU UMa type dwarf novae AK Cnc, WX Cet, AQ Eri, VW Hyi, RZ Leo, TU Men, and HS Vir. All data sets are treated in the same manner, applying a sequence of techniques for each system. The basic ingredients of this sequence are the diagnostic diagram to determine the zero point of the orbital phase, and Doppler tomography to visualise the emission distribution. We furthermore introduce a new qualitative way of to evaluate the Doppler fit, by comparing the line profile of the reconstructed with the original spectrum in the form of the V/R plot. We present the results of the analysis in the compact form of an atlas, allowing a direct comparison of the emission distribution in our targets. Although most of the data sets were not taken with the intention of a line-profile analysis, we obtain significant results and are able to indicate the type of the additional emission in these systems. Our objects should have in principle very similar physical properties, i.e. they cover only a small range in orbital periods, mass ratios, and mass-transfer rates. Nevertheless, we find a large variety of phenomena both with respect to the individual systems and also within individual data sets of the same object. This includes `canonical' additional emission components from the secondary star and the bright spot, but also emission from the leading side of the accretion disc.

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arXiv2003

GZ Cancri: a cataclysmic variable at the lower edge of the period gap

We present calibrated photometry and time-resolved spectroscopy of the cataclysmic variable GZ Cnc. Radial velocities of the H-alpha emission line reveal an orbital period of 0.08825(28) d, or 2.118(07) h, placing the system at the lower edge of the period gap. One of our observations catches the system on the rise to an overlooked, possibly small-amplitude, outburst. At certain phases during this stage the profiles of the emission lines are distorted by a high velocity absorption component. We discuss this phenomenon in the context of the recent suggestion that the long-term lightcurve of GZ Cnc resembles those of intermediate polars.

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arXiv2003

The emission distribution of RR Pictoris

We present time-resolved optical spectroscopy of the old nova RR Pic. Two emission lines (Halpha and He I) are present in the observed part of the spectrum and both show strong variability. Halpha has been used for Doppler tomography in order to map the emission distribution in this system for the first time. The resulting map shows the emission from the disc as well as two additional emission sources on the leading and trailing side of the disc. Furthermore we find evidence for the presence of either a disc-overflow or an asymmetric outflow from the binary with velocities up to +- 1200km/s. The origin of the outflow would be the emission source on the leading side of the accretion disc.

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arXiv2002

On the orbital period of the cataclysmic variable V592 Herculis

We present a spectroscopic study of the long-recurrence-time dwarf nova V592 Herculis based on observations obtained during its August 1998 superoutburst. From the analysis of the radial velocities of the Halpha emission line we find a most likely orbital period of 85.5 +- 0.4 minutes, but the 91.2 +- 0.6 minutes alias cannot be completely discarded. Both periods imply a very small period excess and supports the brown-dwarf like nature of the secondary star.

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