Publications as author and co-author


VSX J003909.7+611233: a new gamma Doradus variable in Cassiopeiae?

By D. Boyd et al.

Accepted for publication in Journal of the British Astronomical Association
(Submitted on 28 Jan 2010) 
http://arxiv.org/abs/1001.5277

Abstract :

We report the discovery of a new 13th magnitude variable in Cassiopeia close to the variable KP Cas. Analysis of 6 days of intensive photometry shows regular modulation with amplitude 0.024 mag and period 0.43815(31) d. Assuming little or no reddening, its colour indicates a spectral type around F0. On the available evidence, we consider it most likely to be a new gamma Doradus star. The variable has been registered in the International Variable Star Index with the identifier VSX J003909.7+611233.

CX Lyrae 2008 Observing Campaign

By P. de Ponthière et al.

JAAVSO Volume 37, 2009
http://www.aavso.org/publications/ejaavso/v37n2/117.pdf
or
http://adsabs.harvard.edu/abs/2009JAVSO..37..117D

Abstract :

The Blazhko effect in CX Lyr has been reported for the first time by Le Borgne et al. (2007). The authors have pointed out that the Blazhko period was not evaluated accurately due to dataset scarcity. The possible period values announced were 128 or 227 days. A newly conducted four-month observing campaign in 2008 (fifty-nine observation nights) has provided fourteen times of maximum. From a period analysis of measured times of maximum, a Blazhko period of 62 ± 2 days can be suggested. However, the present dataset is still not densely sampled enough to exclude that the measured period is still a modulation of the real Blazhko period. Indeed the shape of the (O–C) curve does not repeat itself exactly during the campaign duration.

CCD photometry of the first observed superoutburst of KP Cassiopeiae in 2008 October

By D. Boyd et al.

http://arxiv.org/abs/0907.0092

July 1st 2009

Abstract :

We report CCD photometry and analysis of the first observed superoutburst of the SU UMa-type dwarf nova KP Cassiopeiae during 2008 October. We observed a distinct shortening of the superhump period at superhump cycle 15. Before that point Psh was 0.08556(3) d and afterwards it evolved from 0.08517(2) d to 0.08544(3) d with a rate of period change dPsh/dt = 3.2(2) * 10-5. We measured the likely orbital period as 0.0814(4) d placing KP Cas just below the period gap. The superhump period excess ε is 0.048(5) and, empirically, the mass ratio q is 0.20(2). The superoutburst lasted between 8 and 12 days, peaked close to magnitude 13 with an amplitude above quiescence of 5 magnitudes, and faded for 4 days at a rate of 0.14 mag/d. Close monitoring following the end of the superoutburst detected a single normal outburst 60 days later which reached magnitude 14.7 and lasted less than 3 days.

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae

By Taichi Kato et al.
http://arxiv.org/abs/0905.1757

PASJ Publ. Astron. Soc Japan, May 2009

Abstract :

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0.08 d show positive period derivatives. Contrary to the earlier claim, we found no clear evidence for variation of period derivatives between superoutburst of the same object. We present an interpretation that the lengthening of the superhump period is a result of outward propagation of the eccentricity wave and is limited by the radius near the tidal truncation. We interprete that late stage superhumps are rejuvenized excitation of 3:1 resonance when the superhumps in the outer disk is effectively quenched. Many of WZ Sge-type dwarf novae showed long-enduring superhumps during the post-superoutburst stage having periods longer than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently, mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives and are excellent candidate for the systems around or after the period minimum of evolution of cataclysmic variables (abridged).

VSX J074727.6+065050: a new WZ Sagittae star in Canis minor

By J. Shears et al.
http://arxiv.org/abs/0905.0061

Journal of the British Astronomical Association, May 2009

Abstract :

We present photometry of the first reported superoutburst of the dwarf nova VSX J074727.6+065050 during 2008 January and February. At its brightest the star reached magnitude 11.4 and this was followed by a slow decline at 0.09 mag/d for 19 days, corresponding to the plateau phase. There was then a rapid decline at 1.66 mag/d to a temporary minimum at magnitude 16.6 where it stayed for 2 to 3 days after which there were six remarkable echo outbursts before the star gradually faded back towards quiescence at ~magnitude 19.5. The overall outburst amplitude was at least 8 magnitudes and it lasted more than 80 days. During the plateau phase we observed common superhumps with Psh = 0.06070(6) d, but the period increased to Psh = 0.06151(5) d coinciding with the end of the plateau phase and the onset of the rapid decline. This corresponds to a continuous period change with P^dot = +4.4(9) x 10-5. During the echo outbursts there was a superhump regime with Psh = 0.06088(49) d. Evidence is presented which is consistent with the star being a member of the WZ Sge family of dwarf novae.

SDSS J080434.20+510349.2: Eclipsing WZ Sge-Type Dwarf Nova with Multiple Rebrightenings

By T. Kato, E. Pavlenko et al.
http://arxiv.org/abs/0903.1685
 
PASJ March 2009

Abstract :

We observed the 2006 superoutburst of SDSS J080434.20+510349.2 during its plateau phase, rebrightening phase, and post-superoutburst final decline. We found that this object is a grazing eclipsing system with a period of 0.0590048(2) d. Well-defined eclipses were only observed during the late stage of the superoutburst plateau and the depth decreased during the subsequent stages. We determined the superhump period during the superoutburst plateau to be 0.059539(11) d, giving a fractional superhump excess of 0.90(2)%. During the rebrightening and post-superoutburst phases, persisting superhumps with periods longer than those of superhumps during the plateau phase: 0.059632(6) during the rebrightening phase and 0.05969(4) d during the final fading. This phenomenon is very well in line with the previously known long-period "late superhumps" in GW Lib, V455 And and WZ Sge. The amplitudes of orbital humps between different states of rebrightenings suggest that these humps do not arise from the classical hot spot, but are more likely a result of projection effect in a high-inclination system. There was no clear evidence for the enhanced hot spot during the rebrightening phase. We also studied previously reported "mini-outbursts" in the quiescent state and found evidence that superhumps were transiently excited during these mini-outbursts. The presence of grazing eclipses and distinct multiple rebrightenings in SDSS J080434.20+510349.2 would provide a unique opportunity to understanding the mechanism of rebrightenings in WZ Sge-type dwarf novae.

Observations of the first confirmed superoutburst of SDSS J080434.20+510349.2 in 2006 March

By J.Shears, G. Klingenberg and P. de Ponthière

http://arxiv.org/abs/0705.4616
Journal of British Astronomical Association (May 2007)

Abstract :

During 2006 March the first confirmed superoutburst of the dwarf nova SDSS J080434.20+510349.2 was observed using unfiltered CCD photometry. Time-series photometry revealed superhumps with a period of 0.0597 +/- 0.0011 d and an amplitude of 0.2 magnitude, thereby independently establishing its UGSU classification. Following the decline from a peak magnitude of 13.1, at least two rebrightening events were observed. Evidence is presented which is consistent with the star being a member of the UGWZ sub-class.

 

Discovery of Very Bright, Nearby Gravitational Microlensing Event

By J. Patterson et al.

http://arxiv.org/abs/astro-ph/0703125
March 2007

Abstract :

We report the serendipitous detection of a very bright, very nearby microlensing event. In late October 2006, an otherwise unremarkable A0 star at a distance ~1 kpc (GSC 3656-1328) brightened achromatically by a factor of nearly 40 over the span of several days and then decayed in an apparently symmetrical way. We present a light curve of the event based on optical photometry from the Center for Backyard Astrophysics and the All Sky Automatic Survey, as well as near-infrared photometry from the Peters Automated Infrared Imaging Telescope. This light curve is well-fit by a generic microlensing model. We also report optical spectra, and Swift X-ray and UV observations that are consistent with the microlensing interpretation. We discuss and reject alternative explanations for this variability. The lens star is probably a low-mass star or brown dwarf, with a relatively high proper motion of >20 mas/yr, and may be visible using precise optical/infrared imaging taken several years from now. We demonstrate that a modest, all-sky survey telescope could detect ~10 such events per year, which would enable searches for very low-mass planetary companions to relatively nearby stars.

 

The detection of the WZ Sge-type nature of the dwarf novae ASAS 023322-1047.0 and ASAS 102522-1542.4 by the Center for Backyard Astrophysics.

By T. Vanmunster et al.

http://www.socastrosci.org/2006%20papers/Vanmunster_WZSgeDwarfNovae.pdf
Proceedings for the 25th Annual Conference of the Society for Astronomical Siemces (May 2006)

Abstract :

We present the results of a detailed analysis of 13,116 time-series CCD photometry observations of the cataclysmic variable stars ASAS 023322-1047.0 and ASAS 102522-1542.4, collected during 175.1 hours over 23 nights early 2006, by 9 observers. We report a/o the detection of outburst orbital humps and common superhumps, establishing the variables as genuine new members of the rare class of WZ Sge-type dwarf novae. Our observations furthermore provide an excellent basis to illustrate how the pro-am partnership of the Center for Backyard Astrophysics is implemented in practice. © 2006 Society for Astronomical Science.

 

Other contributions

Late-Type Near-Contact Eclipsing Binary [HH97] FS Aur-79

By S.J. Austin, J.W. Robertson et al.

http://arxiv.org/abs/astro-ph/0702171

Abstract:

The secondary photometric standard star #79 for the FS Aur field (Henden & Honeycutt 1997) designated as [HH97] FS Aur-79 (GSC 1874 399) is a short period (0.2508 days) eclipsing binary whose light curve is a combination of the beta Lyr and BY Dra type variables. High signal-to-noise multi-color photometry were obtained using the USNO 1-m telescope. These light curves show asymmetry at quadrature phases (O'Connell effect), which can be modeled with the presence of star spots. A low resolution spectrum obtained with the 3.5-m WIYN telescope at orbital phase 0.76 is consistent with a spectral type of dK7e and dM3e. A radial velocity curve for the primary star was constructed using twenty-four high resolution spectra from the 9.2 m HET. Spectra show H-alpha and H-beta in emission confirming chromospheric activity and possibly the presence of circumstellar material. Binary star models that simultaneously fit the U, B, V, R and RV curves are those with a primary star of mass 0.59+-0.02 Msun, temperature 4100+-25 K, mean radius of 0.67 Rsun, just filling its Roche lobe and a secondary star of mass 0.31+-0.09 Msun, temperature 3425+-25 K, mean radius of 0.48 Rsun, just within its Roche lobe. An inclination angle of 83+-2 degrees with a center of mass separation of 1.62 Rsun is also derived. Star spots, expected for a rotation period of less than a day, had to be included in the modeling to fit the O'Connell effect.