Publications as author and co-author

TU Comae Berenices : Blazhko RR Lyrae Star in a Potential Binary System

By Pierre de Ponthiere, Franz-Joseph Hambsch, Kenneth Menzies, Richard Sabo
published in JAAVSO 2016 Volume 44
We present the results of a photometry campaign of TU Com performed over a five-year time span. The analysis showed that the possible Blazhko period of 75 days published by the General Catalogue of Variable Stars is not correct. We identified two Blazhko periods of 43.6 and 45.5 days. This finding is based on measurement of 124 light maxima. A spectral analysis of the complete light curve confirmed these two periods. Besides the Blazhko amplitude and phase modulations, another long term periodic phase variation has been identified. This long term periodic variation affects the times of maximum light only and can be attributed to a light-travel time effect due to orbital motion of a binary system. The orbital parameters have been estimated by a nonlinear least-square fit applied to the set of (O-C) values. The Levenberg-Marquart algorithm has been used to perform the nonlinear least-square fit. The tentative orbital parameters include an orbital period of 1676 days, a minimal semi-major axis of 1.55 AU, and a small eccentricity of 0.22. The orbital parameter estimation also used 33 (O-C) values obtained from the SWASP survey database. Spectroscopic radial velocity measurements are needed to confirm this binarity. If confirmed, TU Com would be the first Blazhko RR Lyrae star detected in a binary system.

AL Pictoris and FR Piscium: Two Regular Blazhko RR Lyrae Stars

By Pierre de Ponthiere, Franz-Joseph Hambsch, Kenneth Menzies, Richard Sabo
Published in JAAVSO 2014 Volume 42
The results presented are a continuation of observing campaigns conducted by a small group of amateur astronomers interested in the Blazhko effect of RR Lyrae stars. The goal of these observations is to confirm the RR Lyrae Blazhko effect and to detect any additional Blazhko modulation which cannot be identified from all sky survey data-mining. The Blazhko effect of the two observed stars is confirmed, but no additional Blazhko modulations have been detected. The observation of the RR Lyrae star AL Pictoris during 169 nights was conducted from San Pedro de Atacama (Chile). From the observed light curve, 49 pulsation maxima have been measured. Fourier analyses of (O-C), magnitude at maximum light (Mmax), and the complete light curve have provided a confirmation of published pulsation and Blazhko periods, 0.548622 and 34.07 days, respectively. The second multi-longitude observation campaign focused on the RR Lyrae star FR Piscium and was performed from Europe, the United States, and Chile. Fourier analyses of the light curve and of 59 measured brightness maxima have improved the accuracy of pulsation and Blazhko periods to 0.45568 and 51.31 days, respectively. For both stars, no additional Blazhko modulations have been detected.

Multi-Longitude Observation Campaign of KV Cancri: an RR Lyrae star with irregular Blazhko modulations

By Pierre de Ponthiere, Michel Bonnardeau, Franz-Joseph Hambsch, Tom Krajci, Kenneth Menzies, Richard Sabo
JAAVSO 2014 Volume 42, 53
We present the results of multi-longitude observations of KV Cancri, an RR Lyrae star showing an irregular Blazhko effect. With a pulsation period of 0.50208 day, the times of light curve maxima are delayed by 6 minutes per day. This daily delay regularly leads to long periods of time without maximum light curve observations for a given site. To cope with this observing time window problem, we have organized a multi-longitude observation campaign including a telescope of the AAVSONet. From the observed light curves, 92 pulsation maxima have been measured covering about six Blazhko periods. The Fourier analysis of magnitudes at maximum light has revealed a main Blazhko period of 77.6 days and also a secondary period of 40.5 days. A Fourier analysis of (O-C) values did not show the secondary Blazhko period. The frequency spectrum of the complete light curve, from a Fourier analysis and successive pre-whitening with PERIOD04, has shown triplet structures around the two Blazhko modulation frequencies but with slightly different periods (77.8 and 42.4 days). The second Blazhko frequency is statistically not a harmonic of the main Blazhko frequency. Besides the two Blazhko modulations KV Cnc presents other particularities like irregularities from Blazhko cycle to cycle and very fast magnitude variations which can reach a maximum of 2.5 magnitudes per hour over a period of 15 minutes. This campaign shows that regular observations by amateur astronomers remain important. Indeed such a detailed characterization of the Blazhko effect could not be obtained from large-scale surveys, as cooperative long time-series observations are needed.

V0784 Ophiuchi: an RR Lyrae star with multiple Blazhko modulations

By Ponthiere, Franz-Josef (Josch) Hambsch, Tom Krajci, Kenneth Menzies
JAAVSO 2013 Volume 41, 214

The results of an observation campaign of V0784 Ophiuchi over a time span of two years have revealed a multi-periodic Blazhko effect. A Blazhko effect for V0784 Ophiuchi has not been reported previously. From the observed light curves, 60 pulsation maxima have been measured. The Fourier analyses of the (O-C) values and of magnitudes at maximum light have revealed a main Blazhko period of 24.51 days but also two other secondary Blazhko modulations with periods of 34.29 and 31.07 days. A complete light curve Fourier analysis with PERIOD04 has shown triplet structures based on main and secondary Blazhko frequencies close to the reciprocal of Blazhko periods measured from the 60 pulsation maxima.

V1820 Orionis : an RR Lyrae star with strong and irregular Blazhko effect

By Ponthiere, Franz-Josef (Josch) Hambsch, Tom Krajci, Kenneth Menzies, Patrick Wils
JAAVSO 2013 Volume 41, 58
The Blazhko effect in V1820 Orionis and its period were reported for the first time by Wils et al. (2006) from a data analysis of the Northern Sky Variability Survey. The results of additional V1820 Orionis observations over a time span of 4 years are presented herein. From the observed light curves, 73 pulsation maxima have been measured. The times of light maxima have been compared to ephemerides to obtain the (O-C) values. The Blazhko period (27.917 +/- 0.002 d) has been derived from light curve Fourier analysis and from ANOVA analyses of the (O-C) values and of magnitudes at maximum light (Mmax). During one Blazhko cycle, a hump in the ascending branch of the light curve was clearly identified and has also created a double maximum in the light curve. The frequency spectrum of the light curve, from a Fourier analysis with Period04, has revealed triplet, quintuplet structures, and a second Blazhko weak modulation (period = 34.72 +/-0.01 d). V1820 Orionis can be ranked as a strongly modulated star based on its observed amplitude and phase variations. The amplitude ratio of the largest triplet component to main pulsation component is quite large: 0.34.

GEOS RR Lyrae Survey: Blazhko Period Measurement of Three RRab Stars - CX Lyrae, NU Aurigae, and VY Coronae Borealis

By Ponthiere et al.
JAAVSO 2012 Volume 40, 904
We present the results of collaborative observations of three RR Lyrae stars (CX Lyr, NU Aur, and VY CrB) which have a strong Blazhko effect. This work has been initiated and performed in the framework of the GEOS RR Lyr Survey (Groupe Européen d´Observations Stellaires). From the measured light curves, we have determined the times and the magnitudes at maximum. The times of maxima have been compared to ephemerides to obtain the (O−C) values and from a period analysis of these (O−C) values, the Blazhko period is derived. The Blazhko periods of NU Aur (114.8 days) and VY CrB (32.3 days) are reported here for the first time and a more accurate period for CX Lyr (68.3 days) has been obtained. The three stars are subject to strong Blazhko effect, but this effect has different characteristics for each of them. When we compare the variations of magnitude at maximum and variations of (O−C) values with respect to the Blazhko phase, these variations are in phase, in opposition, or even in quadrature.

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)
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

The GEOS RR Lyr survey: Analysis of light curve of the RR-Lyr star DY And

J.F.Le Borgne, J.M. Llapasset, J. Nicolas, P. de Ponthiere, M. Serrau
Geos circular September 16th 2009
We analyse new observations of the under-studied RR-Lyr star DY And. These observations have been made between 2006 November 2 and 2008 November 28 with 20 to 30cm telescopes and CCD cameras. These observations allow to affine the period of the star and to set mean elements in agreement with former observations: 2454050.362 + 0.6030824 E We show that a Blazhko effect exists with a period which remains to be determined but which might be of the order of 230 days. More observations are necessary.

CX Lyrae 2008 Observing Campaign Ponthière et al.
JAAVSO 2009 Volume 37, 117
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.
July 1st 2009
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.
PASJ Publ.Astron. Soc Japan, May 2009
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

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

By J. Shears et al.
Journal of the British Astronomical Association, May 2009
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.
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
Journal of British Astronomical Association (May 2007)
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.
March 2007
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.
Proceedings for the 25th Annual Conference of the Society for Astronomical Siemces (May 2006)
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.

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

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