arXiv subjects

Albert Bruch

Publications and source records attributed to Albert Bruch.

At least 19 recordsLinked to original sources

arXiv2026

IPHAS J190812.63+045728.1: A deeply eclipsing, X-ray bright cataclysmic variable with frequent outbursts

We present a multi-wavelength characterization of IPHAS J190812.63+045728.1. Independently discovered by us after being serendipitously observed by XMM-Newton, followed up with optical photometry with SPARC4/OPD and spectroscopy with GMOS/Gemini South, and exploring archival TESS and ZTF observations, we reveal the system to be an eclipsing accreting white dwarf (WD) system with an orbital period of 5.073 h. The deep optical and flat-bottomed X-ray eclipses completely occult the WD and the accretion disk, providing a model-independent, uncontaminated view of the donor star which we classify as an M2.3 dwarf with a mass of $\sim 0.50\,M_\odot$. The system is a modestly luminous (L$_{x;0.3-10 keV} \sim$ 1.7 $\times$ 10$^{32}$ erg s$^{-1}$) hard thermal (consistent with a shock-heated plasma cooling down from $k$T $\sim$ 26 keV) X-ray source. While these X-ray properties are typical of low luminosity intermediate polars (IPs), long-term archival photometry reveals frequent, large-amplitude outbursts ($\Delta m \sim 2$ mag in the ZTF $zr$ band) that are the typical characteristics of dwarf novae, and would be unusual for IPs. The weakness of the HeII $\lambda$4686 emission line does not allow us to decide between the IP and the dwarf nova scenarios. On the other hand, the optical and X-ray light curves do not exhibit periodic variations caused by the WD rotation. If the system is indeed an IP, the accretion geometry is likely unusual while the dwarf nova-like outbursts indicating disk instabilities would make IPHAS J190812.63+045728.1 a benchmark for testing disk instability models in the presence of magnetically truncated accretion disks. Otherwise, the system is a dwarf nova with X-ray properties at the extreme end of its class.

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arXiv2024

The AH Pictoris syndrome: Continuous trains of stunted outbursts in novalike variables

Novalike variables are a subgroup of cataclysmic variables (CVs) that -- unlike dwarf novae -- do not exhibit strong brightenings in their long-term light curves. Variations over time scales of weeks, months or years are mostly restricted to irregular low-amplitude modulations. However, some of them occasionally suffer from so-called stunted outbursts, that is, small-scale brightenings of less than a magnitude lasting for a couple of days to weeks. There is no consensus about the physical mechanisms behind these outbursts. Here I discuss the common properties of a group of novalike variables (which I call AH~Pictoris stars after its most prominent member) that exhibit a continuous train of successive stunted outbursts over their entire observational history, or at least for several years. The outburst amplitudes are stable in a given system, always ranging between 0.5 and 1~mag in the visual band. The outburst intervals, at an overall range between 12 and 30 days, and the outburst profiles can gradually evolve, but no sudden changes are observed. On shorter time scales the orbital waveforms are not only surprisingly similar, but also evolve in the same way over the outburst cycle. All AH~Pic stars have absolute visual magnitudes in the overlap region between absolute magnitudes of all novalike variables and of quiescent dwarf novae above the CV period gap. So far, I identified seven novalike variables with the consistent photometric behavior which may be termed the AH~Pic syndrome. Several more systems may be related objects. The relationship to the anomalous Z~Cam stars is discussed.

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arXiv2023

TESS light curves of cataclysmic variables -- III -- More superhump systems among old novae and novalike variables

Continuing previous work on the identification and characterization of periodic and non-periodic variations in long and almost uninterrupted high cadence light curves of cataclysmic variables observed by the TESS mission, the results on 23 novalike variables and old novae out of sample of 127 suchsystems taken from the Ritter & Kolb catalogue are presented. All of them exhibit at least at some epochs either positive or negative (or both) superhumps, and in 19 of them superhumps were detected for the first time. The basic properties of the superhumps such as their periods, their appearance and disappearance, and their waveforms are explored. Together with recent reports in the literature, this elevates the number of known novalike variables and old novae with superhumps by more than 50%. The previous census of superhumps and the Stolz-Schoembs relation for these stars are updated. Attention is drawn to superhump properties in some stars which behave differently from the average, as well as to positive superhumps in high mass ratio systems which defy theory. As a byproduct, the orbital periods of 13 stars are either improved or newly measured, correcting previously reported erroneous values.

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arXiv2022

TESS light curves of cataclysmic variables -- II: Superhumps in old novae and novalike variables

Superhumps are among the abundant variable phenomena observed in the light curves of cataclysmic variables (CVs). They come in two flavours as positive and negative superhumps, distinguished by periods slightly longer or shorter, respectively, than the orbital periods of these interacting binary systems. Positive superhumps are ubiquitous in superoutbursting short period dwarf novae of the SU~UMa type but are less common in longer period systems with accretion disks in a permanent bright state such as novalike variables and most old novae. Negative superhumps do not seem not to have a preference for a particular type of CV. Here, I take advantage of the long high cadence light curves provided by TESS for huge number of stars, selecting all old novae and novalike variables with past reported superhumps for which TESS light curves are available and have not yet been analysed in previous publications in order to study their superhump behaviour. In combination with information taken from the literature the results enable to compile the most complete census of superhumps in these stars so far. As a corollary, for the eclipsing systems in the present sample of objects eclipse epochs derived from the TESS light curves and in some cases from archival light curves are listed and used to update orbital ephemeris and to discuss period changes.

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arXiv2022

TESS light curves of cataclysmic variables I -- Unknown periods in long-known stars

Cataclysmic variables (CVs) exhibit a plethora of variable phenomena many of which require long, uninterrupted light curves to reveal themselves in detail. The month long datasets provided by TESS are well suited for this purpose. TESS has the additional advantage to have observed a huge number of stars, among them many CVs. Here, a search for periodic variations in a sample of CVs of the novalike and old novae subtypes is presented. In 10 of the 15 targets either previously unseen positive or negative superhumps or unusual features in known superhumps are identified. The TESS light curves demonstrate that the occurrence of superhumps in these types of CVs is not an exception but quite common. For 8 systems new or improved values for the orbital period are measured. In TV Col the long-sought optical manifestation of the white dwarf spin period is first seen in form of its orbital sideband. The mystery of multiple photometric periods observed in CP Pup in the past is explained by irregularly occurring anomalous states which are reflected in the light curve.

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arXiv2021

Flickering around the outburst cycle in Kepler dwarf novae

Taking advantage of the unparallel quantity and quality of high cadence Kepler light curves of several dwarf novae, the strength of the flickering and the high frequency spectral index of their power spectra are investigated as a function of magnitude around the outburst cycle of these systems. Previous work suggesting that the flickering strength (on a magnitude scale) is practically constant above a given brightness threshold and only rises at fainter magnitudes is confirmed for most of the investigated systems. As a new feature, a hysteresis in the flickering strength is seen in the sense that at the same magnitude level flickering is stronger during decline from outburst than during the rise. A similar hysteresis is also seen in the spectral index. In both cases, it can qualitatively be explained under plausible assumptions within the DIM model for dwarf nova outbursts.

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arXiv2021

Orbital Periods and Waveforms of Dwarf Novae Observed by Kepler

Kepler high cadence data are used to measure the orbital periods and to determine the orbital waveforms of five dwarf novae. A significant improvement of the period of V1504 Cyg is achieved, while for the other systems periods are derived which are compatible with previous determinations. The orbital waveforms of the short period systems V1504 Cyg, V344 Lyr and V516 Lyr are very nearly sinusoidal, while the longer period dwarf nova V447 Lyr appears almost to be a twin of U Gem. The unusual system KIC 9202990 exhibits distinct variations of its waveform as a function of brightness during its outburst cycle.

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arXiv2021

A comparative study of the strength of flickering in cataclysmic variables

Flickering is a universal phenomenon in accreting astronomical systems which still defies detailed physical understanding. It is particularly evident in cataclysmic variables (CVs). Attempting to define boundary conditions for models, the strength of the flickering is measured in several thousand light curves of more than 100 CVs. The flickering amplitude is parameterized by the FWHM of a Gaussian fit to the magnitude distribution of data points in a light curve. This quantity requires several corrections before a comparison between different sources can be made. While no correlations of the flickering strength with simple parameters such as component masses, orbital inclination or period were detected, a dependence on the absolute magnitude of the primary component and on the CV subtype is found. In particular, flickering in VY Scl tpye novalike variables is systematically stronger than in UX UMa type novalikes. The broadband spectrum of the flickering light source can be fit by simple models but shows excess in the $U$ band. When the data permitted to investigate the flickering strength as a function of orbital phase in eclipsing CVs, such a dependence was found, but it is different for different systems. Surprisingly, there are also indications for variations of the flickering strength with the superhump phase in novalike variables with permanent superhumps. In dwarf novae, the flickering amplitude is high during quiescence, drops quickly at an intermediate magnitude when the system enters into (or returns from) an outburst and, on average, remains constant above a given brightness threshold.

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arXiv2020

CTCV J2056-3014: An X-ray-faint Intermediate Polar Harboring An Extremely Fast-spinning White Dwarf

We report on XMM-Newton X-ray observations that reveal CTCV J2056-3014 to be an unusual accretion-powered, intermediate polar (IP) system. It is a member of the class of X-ray-faint IPs whose space density remains unconstrained but potentially very high, with L$_{x,0.3-12 keV}$ of 1.8$\times$10$^{31}$ erg s$^{-1}$. We discovered a coherent 29.6s pulsation in X-rays that was also revealed in our reanalysis of published optical data, showing that the system harbors the fastest-spinning, securely known white dwarf (WD) so far. There is no substantial X-ray absorption in the system. Accretion occurs at a modest rate ($\sim$ 6$\times$10$^{-12}$ M$_{\odot}$ yr$^{-1}$) in a tall shock above the WD, while the star seems to be spinning in equilibrium and to have low magnetic fields. Further studies of CTCV J2056-3014 potentially have broad implications on the origin of magnetic fields in WDs, on the population and evolution of magnetic cataclysmic variables, and also on the physics of matter around rapidly rotating magnetic WDs.

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arXiv2020

Miscellaneous photometric variations in cataclysmic variables: V455 And, SS Cyg, AQ Men, LQ Peg, RW Tri and UX UMa

Cataclysmic variables are among the photometrically most unstable stars in the zoo of stellar objects, exhibiting light variations on all time-scales between millennia and seconds. The literature is full of reports on variable phenomena which often require independent confirmation before they can be accepted as established facts. In this contribution I investigate accounts on miscellaneous variable features observed in six cataclysmic variables, drawing for this purpose largely on archival data, most of which have not been investigated in detail in the past, and complementing these data with some new observations. This enabled to confirm and expand upon some hitherto unconfirmed features in the light curves of these star, as well as the rejection of some others, while in still other cases an unambiguous answer to questions arising from previous papers was not possible.

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arXiv2019

TT Arietis: 40 years of photometry

In an effort to characterize variations on the time scale of hours and smaller during the high and low states of the novalike variable TT Ari, light curves taken over the course of more than 40 yr are analyzed. It is found that the well known negative superhump observed during the high state persists until the present day at an average period of 0.13295 d which is slightly variable from year to year and exhibits substantial amplitude changes. The beat period between superhump and orbital period is also seen. QPOs occur at a preferred quasi-period of 18 -- 25 min and undergo a systematic frequency evolution during a night. The available data permit for the first time a detailed investigation of the low state which is highly structured on time-scales of tens of days. On hourly time scales the light curve exhibits strong variations which are mostly irregular. However, during an interval of several days at the start of the low state, coherent 1.2 mag oscillations with a period of 8.90 h are seen. During the deep low state quiet phases and strong (1.5 -- 3 mag), highly structured flares alternate in irregular intervals of roughly 1 day. The quiet phases are modulated on the orbital period of TT Ari, suggesting reflection of the light of the primary component off the secondary. This is the first time that the orbital period is seen in photometric data.

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arXiv2019

UU Aqr - No superhumps but variations on the time scale of days

Recently, brightness variations occurring on twice the accretion disk precession period in the old nova and permanent superhump system V603 Aql have been observed by Bruch & Cook (2018). In an attempt to detect a similar effect in other cataclysmic variables reported to contain permanent superhumps the novalike variable UU Aqr was observed during 11 nights in September 2018. While no traces of superhumps were seen in the data, rendering the quest for variations related to the disk precession period obsolete, the system exhibits regular variations with a period of ~4 days.

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arXiv2018

Coherent brightness modulations in the dwarf nova AT Cancri

Light curves of the Z Cam type dwarf nova AT Cnc observed during standstill in 2016 and 2018 are analyzed. On the time scale of hours, previous reports on periodicities, in particular the presence of negative superhumps, could not be confirmed. Instead, a modulation with a period equal to the spectroscopic orbital period was detected which we thus interpret as a manifestations of the binary revolution. It enables us to derive a more accurate value of 0.201634 $\pm$ 0.000005 days (or its alias of 0.021580 days) for the period. AT Cnc also exhibits a hitherto unreported modulation of 25.731 $\pm$ 0.005 min, stable in period but not in amplitude over the entire time base of two years of the observations. We tentatively interpret this modulation in the context of an intermediate polar model for the system.

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arXiv2018

Cyclic variations with twice the accretion disk precession period in the old nova V603 Aquilae

A dense series of long and high time resolution light curves of the old nova V603 Aql, covering 22 nights (19 of which are consecutive), are analyzed in order to identify and characterize variations on the time scale of hours and days. The well known 3.5 hour modulation, observed many times in the past and considered to be due to a long lasting, albeit not entirely stable superhump, is recovered at a period of 0.1453 days and an amplitude of 0.062 mag. Most interesting, however, is the detection of highly significant brightness variations with an amplitude of 0.050 mag and a period of 5.85 days which is to a very high precision equal to twice the beat period between the orbital and the superhump period. The latter is generally interpreted as the precession period of an eccentric accretion disk. The origin of these long term variations remains unknown.

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arXiv2017

Photometry of some more neglected bright cataclysmic variables and candidates

As part of an effort to better characterize bright cataclysmic variables (CVs) and related systems which have received little attention in the past light curves of four systems (V504 Cen, KT Eri, Ret 1 and CTCV 2056-3014) are analyzed. For some of these stars no time resolved photometry has been published previously. While flickering is observed in all systems except Ret 1, it is particularly strong in V504 Cen and CTCV 2056-3014. In the latter star, a previously observed 15.4 m period, leading to its tentative classification as an intermediate polar, is probably spurious. Variations on time scales of hundredths of days observed in the pre-outburst light curve of the classical nova KT Eri continue after the outburst but appear not to be strictly periodic. Furthermore, the long term post-outburst light curve exhibits modulations with quasi-periods of quite different length. Thus, these variations cannot be due to aspect related variations in a system with a giant component similar to some recurrent novae. Instead, the system possibly exhibits variations with a period of 0.1952 d which may be orbital. However, any such conclusion still requires confirmation.

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arXiv2017

Orbital variations and outbursts of the unusual variable star V1129 Centauri

The variable star V1129 Cen is classified in the GCVS as being of $β$ Lyr type. Unusual for such stars, it exhibits outbursts roughly once a year, lasting for $\sim$40 days. For this reason, a relationship to the dwarf novae has been suspected. Here, for the first time a detailed analysis of the light curve of the system is presented. Based on observations with high time resolution obtained at the Observatório do Pico dos Dias and on the long term ASAS light curve the orbital variations of the system are studied. They are dominated by ellipsoidal variations and partial eclipses of a probably slightly evolved F2 star in a binary with an orbital period of $21^{\rm h}$ $26^{\rm m}$. Comparison with the characteristics of dwarf novae show that the observational properties of V1129 Cen can be explained if it is just another dwarf novae, albeit with an unusually bright and early type mass donor which outshines the accretion disk and the mass gainer to a degree that many normal photometric and spectroscopic hallmarks of cataclysmic variables remain undetected.

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arXiv2017

Photometry of the three eclipsing novalike variables EC 21178-5417, GS Pav and V345 Pav

As part of a project to better characterize comparatively bright, yet little studied cataclysmic variables time resolved photometry of the three eclipsing novalike variables EC 21178-5417, GS Pav und V345 Pav is presented. Previously known orbital periods are significantly improved and long-term ephemeris are derived. Variations of eclipse profiles, occurring on time scales of days to weeks, are analyzed. Out of eclipse the light curves are characterized by low scale flickering superposed on more gradual variations with amplitudes limited to a few tenths of a magnitude and profiles which at least in EC 21178-5417 and GS Pav roughly follow the same pattern in all observed cycles. Additionally, signs for variations on the time scale of some tens of minutes are seen in GS Pav, most clearly in two subsequent nights when in the first of these a signal with a period of 15.7 min was observed over several hours. In the second night variations with twice this period were seen. While no additional insight could be gained on quasi periodic oscillations (QPOs) and dwarf nova oscillations in EC 21178-5417, previously detected by Warner et al. (2003), and while such oscillations could not be found in V345 Pav, stacked power spectra of GS Pav clearly reveal the presence of QPOs over time intervals of several hours with periods varying between 200 sec and 500 sec in that system.

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arXiv2017

Photometry of the long period dwarf nova GY Hya

Although comparatively bright, the cataclysmic variable GY Hya has not attracted much attention in the past. As part of a project to better characterize such systems photometrically, we observed light curves in white light, each spanning several hours, at Bronberg Observatory, South Africa, in 2004 and 2005, and at the Observatório do Pico dos Dias, Brazil, in 2014 and 2016. These data permit to study orbital modulations and their variations from season to season. The orbital period, already known from spectroscopic observations of Peters & Thorstensen (2005), is confirmed through strong ellipsoidal variations of the mass donor star in the system and the presence of eclipses of both components. A refined period of 0.34723972~(6) days and revised ephemeris are derived. Seasonal changes in the average orbital light curve can qualitatively be explained by variations of the contribution of a hot spot to the system light together with changes of the disk radius. The amplitude of the ellipsoidal variations and the eclipse contact phases permit to put some constraints on the mass ratio, orbital inclination and the relative brightness of the primary and secondary components. There are some indications that the disk radius during quiescence, expressed in units of the component separation, is smaller than in other dwarf novae.

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