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ABSTRACT: Photometric observations obtained by the MOST satellite were used to
characterize optical small scale variability of the young stars FU Ori and Z
CMa. Wavelet analysis for FU Ori reveals the possible existence of several 2-9
d quasi-periodic features occurring nearly simultaneously; they may be
interpreted as plasma parcels or other localized disc heterogeneities revolving
at different Keplerian radii in the accretion disc. Their periods may shorten
slowly which may be due to spiralling in of individual parcels toward the inner
disc radius, estimated at 4.8+/-0.2 R_sun. Analysis of additional multicolour
data confirms the previously obtained relation between variations in the B-V
colour index and the V magnitude. In contrast to the FU Ori results, the
oscillation spectrum of Z CMa does not reveal any periodicities with the
wavelet spectrum possibly dominated by outburst of the Herbig Be component.
03/2013;
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ABSTRACT: The GJ 581 system has been amply studied since its discovery in 2005: the
number of known planets in the system has increased and their orbital
parameters are among the most precisely determined for radial velocity detected
exoplanets. We have acquired MOST space-based photometry during 2007 and 2009,
with the aims of measuring the stellar variability and searching for transits
of GJ 581e, respectively. We quantify our sensitivity to shallow transit
signals using Monte Carlo simulations, and perform a transit search within the
3$\sigma$ transit windows corresponding to both the circular and Keplerian
orbit ephemerides. Our analysis rules out transits for a planet with an orbital
period of 3.15 days (GJ 581 e) having a radius larger than 1.62 $R_{\oplus}$
(or a density lower than 2.39 g cm$^{-3}$ for an orbital inclination of
90$^{\circ}$) to 2$\sigma$ confidence. Thus, if the planet transits, we can
exclude hydrogen, helium and water theoretical model compositions. The MOST
photometry also allows us to rule out transits of GJ 581b within the Keplerian
orbit-derived transit window for impact parameter values smaller than $\sim$0.4
and confirm previous results which exclude transits for this planet within the
circular orbit-derived transit window, for all plausible interior compositions.
We find that the stellar brightness of GJ 581 is stable to within 1%, a
characteristic which is favourable to the development of life in the habitable
zone of the system. In the 2009 photometry, we detect a stellar signal with a
period of 5.586 $\pm$ 0.051 days, which is close to the orbital period of GJ
581b ($P=$5.37 days). However, further monitoring of the system is necessary to
verify the nature of this variation.
11/2012;
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Alexandre David-Uraz, Anthony F. J. Moffat,
André-Nicolas Chené,
Jason F. Rowe,
Nicholas Lange,
David B. Guenther,
Rainer Kuschnig,
Jaymie M. Matthews,
Slavek M. Rucinski,
Dimitar Sasselov,
Werner W. Weiss
[show abstract]
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ABSTRACT: The WR binary CV Serpentis (= WR113, WC8d + O8-9IV) has been a source of
mystery since it was shown that its atmospheric eclipses change with time over
decades, in addition to its sporadic dust production. The first high-precision
time-dependent photometric observations obtained with the MOST space telescope
in 2009 show two consecutive eclipses over the 29d orbit, with varying depths.
A subsequent MOST run in 2010 showed a seemingly asymmetric eclipse profile. In
order to help make sense of these observations, parallel optical spectroscopy
was obtained from the Mont Megantic Observatory (2009, 2010) and from the
Dominion Astrophysical Observatory (2009). Assuming these depth variations are
entirely due to electron scattering in a beta-law wind, an unprecedented 62%
increase in mass-loss rate is observed over one orbital period. Alternatively,
no change in mass-loss rate would be required if a relatively small fraction of
the carbon ions in the wind globally recombined and coaggulated to form carbon
dust grains. However, it remains a mystery as to how this could occur. There
also seems to be evidence for the presence of corotating interaction regions
(CIR) in the WR wind: a CIR-like signature is found in the light curves,
implying a potential rotation period for the WR star of 1.6 d. Finally, a new
circular orbit is derived, along with constraints for the wind collision.
07/2012;
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Diana Dragomir,
Jaymie M. Matthews,
Andrew W. Howard,
Victoria Antoci,
Gregory W. Henry,
David B. Guenther,
John A. Johnson,
Rainer Kuschnig,
Geoffrey W. Marcy, Anthony F. J. Moffat,
Jason F. Rowe,
Slavek M. Rucinski,
Dimitar Sasselov,
Werner W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: The radial velocity-discovered exoplanet HD 97658b was recently announced to
transit, with a derived planetary radius of 2.93 \pm 0.28 R_{Earth}. As a
transiting super-Earth orbiting a bright star, this planet would make an
attractive candidate for additional observations, including studies of its
atmospheric properties. We present and analyze follow-up photometric
observations of the HD 97658 system acquired with the MOST space telescope. Our
results show no transit with the depth and ephemeris reported in the
announcement paper. For the same ephemeris, we rule out transits for a planet
with radius larger than 2.09 R_{Earth}, corresponding to the reported 3\sigma
lower limit. We also report new radial velocity measurements which continue to
support the existence of an exoplanet with a period of 9.5 days, and obtain
improved orbital parameters.
04/2012;
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Joshua N. Winn,
Jaymie M. Matthews,
Rebekah I. Dawson,
Daniel Fabrycky,
Matthew J. Holman,
Thomas Kallinger,
Rainer Kuschnig,
Dimitar Sasselov,
Diana Dragomir,
David B. Guenther, Anthony F. J. Moffat,
Jason F. Rowe,
Slavek Rucinski,
Werner W. Weiss
[show abstract]
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ABSTRACT: We have detected transits of the innermost planet "e" orbiting 55 Cnc
(V=6.0), based on two weeks of nearly continuous photometric monitoring with
the MOST space telescope. The transits occur with the period (0.74 d) and phase
that had been predicted by Dawson & Fabrycky, and with the expected duration
and depth for the crossing of a Sun-like star by a hot super-Earth. Assuming
the star's mass and radius to be 0.963_{-0.029}^{+0.051} M_sun and 0.943 +/-
0.010 R_sun, the planet's mass, radius, and mean density are 8.63 +/- 0.35
Mearth, 2.00 +/- 0.14 Rearth, and 5.9_{-1.1}^{+1.5} g/cm^3. The mean density is
comparable to that of Earth, despite the greater mass and consequently greater
compression of the interior of 55 Cnc e. This suggests a rock-iron composition
supplemented by a significant mass of water, gas, or other light elements.
Outside of transits, we detected a sinusoidal signal resembling the expected
signal due to the changing illuminated phase of the planet, but with a full
range (168 +/- 70 ppm) too large to be reflected light or thermal emission.
This signal has no straightforward interpretation and should be checked with
further observations. The host star of 55 Cnc e is brighter than that of any
other known transiting planet, which will facilitate future investigations.
04/2011;
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[show abstract]
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ABSTRACT: No eclipse has been found in 15 days of almost continuous photometry of Alpha
Leo with accuracy of about 0.0005 mag.
04/2011;
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ABSTRACT: As a continuation of our previous studies in 2007 and 2008, new photometric observations of the T Tauri star TW Hya obtained by the MOST satellite and the All Sky Automated Survey (ASAS) project over 40 d in 2009 with temporal resolution of 0.2 d are presented. A wavelet analysis of the combined MOST–ASAS data provides a rich picture of coherent, intermittent, variable-period oscillations, similarly as discovered in the 2008 data. The periods (1.3–10 d) and systematic period shortening on time-scales of weeks can be interpreted within the model of magnetorotationally controlled accretion processes in the inner accretion disc around the star. Within this model and depending on the assumed visibility of plasma parcels causing the oscillations, the observed shortest oscillation period may indicate the stellar rotation period of 1.3 or 2.6 d, synchronized with the disc at 4.5 or 7.1 R⊙, respectively.
Monthly Notices of the Royal Astronomical Society 01/2011; 410(4):2725 - 2729. · 4.90 Impact Factor
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ABSTRACT: Continuous photometric observations of five young stars obtained by the MOST
satellite in 2009 and 2010 in the Taurus and Lupus star formation regions are
presented. Using light curve modelling under the assumption of internal
invariability of spots, we obtained small values of the solar-type
differential-rotation parameter (k=0.0005-0.009) for three spotted weak-line T
Tau stars, V410 Tau, V987 Tau and Lupus 3-14; for another spotted WTTS, Lupus
3-48, the data are consistent with a rigidly rotating surface (k=0). Three
flares of similar rise (4 min 30 sec) and decay (1 h 45 min) times were
detected in the light curve of Lupus 3-14. The brightness of the classical T
Tau star RY Tau continuously decreased over 3 weeks of its observations with a
variable modulation not showing any obvious periodic signal.
01/2011;
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Gordon E. Sarty,
Tamas Szalai,
Laszlo L. Kiss,
Jaymie M. Matthews,
Kinwah Wu,
Rainer Kuschnig,
David B. Guenther, Anthony F. J. Moffat,
Slavek M. Rucinski,
Dimitar Sasselov,
Werner W. Weiss,
Richard Huziak,
Helen M. Johnston,
Andre Phillips,
Michael C. B. Ashley
[show abstract]
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ABSTRACT: The results of a coordinated space-based photometric and ground-based spectroscopic observing campaign on the enigmatic gamma-ray binary LS 5039 are reported. Sixteen days of observations from the MOST satellite have been combined with high-resolution optical echelle spectroscopy from the 2.3m ANU Telescope in Siding Spring, Australia. These observations were used to measure the orbital parameters of the binary and to study the properties of stellar wind from the O primary. We found that any broad-band optical photometric variability at the orbital period is below the 2 mmag level, supporting the scenario that the orbital eccentricity of the system is near the 0.24 +/- 0.08 value implied by our spectroscopy, which is lower than values previously obtained by other workers. The low amplitude optical variability also implies the component masses are at the higher end of estimates based on the primary's O6.5V((f)) spectral type with a primary mass of ~26 solar masses and a mass for the compact star of at least 1.8 solar masses. The mass loss rate from the O primary was determined to be 3.7E-7 to 4.8E-7 solar masses per year. Comment: Accepted for MNRAS 2010 September 22
09/2010;
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ABSTRACT: Continuous photometric observations of the visible component of the single-line, K2IV spectroscopic binary II Peg carried out by the MOST satellite during 31 consecutive days in 2008 have been analyzed. On top of spot-induced brightness modulation, eleven flares were detected of three distinct types characterized by different values of rise, decay and duration times. The flares showed a preference for occurrence at rotation phases when the most spotted hemisphere is directed to the observer, confirming previous similar reports. An attempt to detect a grazing primary minimum caused by the secondary component transiting in front of the visible star gave a negative result. The brightness variability caused by spots has been interpreted within a cold spot model. An assumption of differential rotation of the primary component gave a better fit to the light curve than a solid-body rotation model. Comment: Accepteed to MNRAS
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Photometry of Wolf-Rayet (WR) stars obtained with the first Canadian space telescope MOST (Microvariability and Oscillations of STars) has revealed multimode oscillations mainly in continuum light that suggest stellar pulsations could be a significant contributing factor to the mass-loss rates. Since the first clear detection of a pulsation period of P = 9.8h in WR123, two other stars have also shown periods of a few days, which must be related to stellar pulsations.
Proceedings of the International Astronomical Union 06/2010; 6:445 - 450.
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ABSTRACT: As recent observations have shown, luminous, hydrogen-rich WN5-7h stars (and their somewhat less extreme cousins, O3f/WN6 stars) are the most massive main-sequence stars known. However, not nearly enough very massive stars have been reliably weighed to yield a clear picture of the upper initial-mass function (IMF). We therefore have carried out repeated high-quality spectroscopy of four new O3f/WN6 and WN5-7h binaries in R136 in the LMC with GMOS at Gemini-South, to derive Keplerian orbits for both components, respectively, and thus to directly determine their masses. We also monitored binary candidates and other, previously unsurveyed stars, to increase the number of very massive stars that can be directly weighed.
Proceedings of the International Astronomical Union 06/2010; 6:497 - 498.
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[show abstract]
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ABSTRACT: We report on the measurement of transit times for the HD 209458 planetary system from photometry obtained with the MOST (Microvariability and Oscillations of Stars) space telescope. Deviations from a constant orbital period can indicate the presence of additional planets in the system that are yet undetected, potentially with masses approaching an Earth mass. The MOST data sets of HD 209458 from 2004 and 2005 represent unprecedented time coverage with nearly continuous observations spanning 14 and 43 days and monitoring three transits and 12 consecutive transits, respectively. The transit times that we obtain show no variations on three scales: (1) no long-term change in P since before 2004 at 25 ms level, (2) no trend in transit timings during the 2005 run, and (3) no individual transit timing deviations above 80 s level. Together with previously published transit times from Agol & Steffen, this allows us to place limits on the presence of additional close-in planets in the system, in some cases down to below an Earth mass. This result, along with previous radial velocity work, now eliminates the possibility that a perturbing planet could be responsible for the additional heat source needed to explain HD 209458b's anomalous low density.
The Astrophysical Journal 12/2008; 682(1):586. · 6.02 Impact Factor
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Jason F. Rowe,
Jaymie M. Matthews,
Sara Seager,
Eliza Miller-Ricci,
Dimitar Sasselov,
Rainer Kuschnig,
David B. Guenther, Anthony F. J. Moffat,
Slavek M. Rucinski,
Gordon A. H. Walker,
and Werner W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: Measuring the albedo of an extrasolar planet provides insight into its atmospheric composition and its global thermal properties, including heat dissipation and weather patterns. Such a measurement requires very precise photometry of a transiting system, fully sampling many phases of the secondary eclipse. Space-based optical photometry of the transiting system HD 209458 from the MOST (Microvariablity and Oscillations of Stars) satellite, spanning 14 and 44 days in 2004 and 2005, respectively, allows us to set a sensitive limit on the optical eclipse of the hot exosolar giant planet in this system. Our best fit to the observations yields a flux ratio of the planet and star of 7 ± 9 ppm (parts per million), which corresponds to a geometric albedo through the MOST bandpass (400-700 nm) of Ag = 0.038 ± 0.045. This gives a 1 σ upper limit of 0.08 for the geometric albedo and a 3 σ upper limit of 0.17. HD 209458b is significantly less reflective than Jupiter (for which Ag would be about 0.5). This low geometric albedo rules out the presence of bright reflective clouds in this exoplanet's atmosphere. We determine refined parameters for the star and exoplanet in the HD 209458 system based on a model fit to the MOST light curve.
The Astrophysical Journal 12/2008; 689(2):1345. · 6.02 Impact Factor
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Bryce Croll,
Gordon A H Walker,
Rainer Kuschnig,
Jaymie M Matthews,
Jason F Rowe,
Andrew Walker,
Slavek M Rucinski,
Artie P Hatzes,
William D Cochran,
Russell M Robb,
David B Guenther, Anthony F J Moffat,
Dimitar Sasselov,
Werner W Weiss
[show abstract]
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ABSTRACT: The Microvariability and Oscillations of STars (MOST) photometric satellite observed three rotations of Eri continuously in late 2005. We detected two spots (Ám $ 0:01) at different latitudes (20N0, 31N5) revolving with different periods (11.35 days, 11.55 days), from which we derive a differential rotation coefficient, k ¼ 0:11 þ:03 À:02 , in agreement with the prediction by Brown and coworkers for a young Sun-like star having roughly twice the solar angular velocity. The light curve was analyzed with the program StarSpotz, a modification of SPOTMODEL by Ribárik and coworkers. The best-fitting value for the inclination angle i ¼ 30 AE 3 is compatible with inclinations already estimated for the disk ($25) and planetary orbit (26N2). The inclination also leads to an equatorial rotation speed of 3.42 km s À1 and the photometric value of v sin i ¼ 1:7 km s À1 . When compared with spectroscopically determined values, the photometric v sin i allows, in principle, an independent estimate of the macroturbulent ve-locity. Both spots would have distorted the radial velocity curve $AE10 m s À1 by the Rossiter-McLaughlin effect, which is similar to the stellar radial velocity ''noise'' detected by others. Details of the StarSpotz model and of the uniqueness tests that we applied in order to arrive at a best solution and realistic estimates of errors in the derived parameters are given.
The Astrophysical Journal 12/2008; 648(1). · 6.02 Impact Factor
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[show abstract]
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ABSTRACT: We present space-based photometry of the transiting exoplanetary system HD 209458 obtained with the Microvariablity and Oscillations of Stars (MOST) satellite, spanning 14 days and covering 4 transits and 4 secondary eclipses. The HD 209458 photometry was obtained in MOST's lower precision direct imaging mode, which is used for targets in the brightness range 6.5 ≥ V ≥ 13. We describe the photometric reduction techniques for this mode of observing, in particular the corrections for stray earthshine. We do not detect the secondary eclipse in the MOST data, to a limit in depth of 0.053 mmag (1 σ). We set a 1 σ upper limit on the planet-star flux ratio of 4.88 × 10-5 corresponding to a geometric albedo upper limit in the MOST bandpass (400-700 nm) of 0.25. The corresponding numbers at the 3 σ level are 1.34 × 10-4 and 0.68, respectively. HD 209458b is half as bright as Jupiter in the MOST bandpass. This low geometric albedo value is an important constraint for theoretical models of the HD 209458b atmosphere, in particular ruling out the presence of reflective clouds. A second MOST campaign on HD 209458 is expected to be sensitive to an exoplanet albedo as low as 0.13 (1 σ), if the star does not become more intrinsically variable in the meantime.
The Astrophysical Journal 12/2008; 646(2):1241. · 6.02 Impact Factor
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Eliza Miller-Ricci,
Jason F. Rowe,
Dimitar Sasselov,
Jaymie M. Matthews,
Rainer Kuschnig,
Bryce Croll,
David B. Guenther, Anthony F. J. Moffat,
Slavek M. Rucinski,
Gordon A. H. Walker,
and Werner W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: We have measured transit times for HD 189733b passing in front of its bright (V = 7.67), chromospherically active, and spotted parent star. Nearly continuous broadband optical photometry of this system was obtained with the Microvariability and Oscillations of Stars (MOST) space telescope during 21 days in 2006 August, monitoring 10 consecutive transits. We have used these data to search for deviations from a constant orbital period which can indicate the presence of additional planets in the system that are as yet undetected by Doppler searches. There are no transit timing variations above the level of ±45 s, ruling out super-Earths (of masses 1-4 M⊕) in the 1:2 and 2:3 inner resonances, and planets of 20 M⊕ in the 2:1 outer resonance of the known planet. We also discuss complications in measuring transit times for a planet that transits an active star with large starspots, and how the transits can help constrain and test spot models. This has implications for the large number of such systems expected to be discovered by the COROT and Kepler missions.
The Astrophysical Journal 12/2008; 682(1):593. · 6.02 Impact Factor
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Theodor Pribulla,
Slavek Rucinski,
Jaymie M. Matthews,
Thomas Kallinger,
Rainer Kuschnig,
Jason F. Rowe,
David B. Guenther, Anthony F. J. Moffat,
Dimitar Sasselov,
Gordon A. H. Walker,
Werner W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: We present two series of MOST (Microvariability and Oscillations of STars) space-based photometry, covering nearly continuously 10 d in 2004 and 30 d in 2007, of selected variable stars in the upper main sequence of the old open cluster M67. New high-precision light curves were obtained for the blue straggler binary/triple systems AH Cnc, ES Cnc and EV Cnc. The precision and phase coverage of ES Cnc and EV Cnc is by far superior to any previous observations. The light curve of ES Cnc is modelled in detail, assuming two dark photospheric spots and Roche geometry. An analysis of the light curve of AH Cnc indicates a low mass ratio (q∼ 0.13) and a high inclination angle for this system. Two new long-period eclipsing binaries, GSC 814−323 and HD 75638 (non-members of M67) were discovered. We also present ground-based DDO spectroscopy of ES Cnc and of the newly found eclipsing binaries. Especially interesting is HD 75638, a member of a visual binary, which must itself be a triple or a higher multiplicity system. New light curves of two δ Scuti pulsators, EX Cnc and EW Cnc, have been analysed leading to detection of 26 and eight pulsation frequencies of high temporal stability.
Monthly Notices of the Royal Astronomical Society 11/2008; 391(1):343 - 353. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: MOST (Microvariability & Oscillations of STars) and ASAS (All Sky Automated Survey) observations have been used to characterize photometric variability of TW Hya on time scales from a fraction of a day to 7.5 weeks and from a few days to 8 years, respectively. The two data sets have very different uncertainties and temporal coverage properties and cannot be directly combined, nevertheless, they suggests a global variability spectrum with "flicker noise" properties, i.e. with amplitudes a ~ 1/sqrt(f), over >4 decades in frequency, in the range f = 0.0003 to 10 cycles per day (c/d). A 3.7 d period is clearly present in the continuous 11 day, 0.07 d time resolution, observations by MOST in 2007. Brightness extrema coincide with zero-velocity crossings in periodic (3.56 d) radial velocity variability detected in contemporaneous spectroscopic observations of Setiawan et al. (2008) and interpreted as caused by a planet. The 3.56/3.7 d periodicity was entirely absent in the second, four times longer MOST run in 2008, casting doubt on the planetary explanation. Instead, a spectrum of unstable single periods within the range of 2 - 9 days was observed; the tendency of the periods to progressively shorten was well traced using the wavelet analysis. The evolving periodicities and the overall flicker-noise characteristics of the TW Hya variability suggest a combination of several mechanisms, with the dominant ones probably related to the accretion processes from the disk around the star. Comment: MNRAS submitted
09/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We present two series of MOST (Microvariability & Oscillations of STars) space-based photometry, covering nearly continuously 10 days in 2004 and 30 days in 2007, of selected variable stars in the upper Main Sequence of the old open cluster M67. New high-precision light curves were obtained for the blue-straggler binary/triple systems AH Cnc, ES Cnc and EV Cnc. The precision and phase coverage of ES Cnc and EV Cnc is by far superior to any previous observations. The light curve of ES Cnc is modelled in detail, assuming two dark photospheric spots and Roche geometry. An analysis of the light curve of AH Cnc indicates a low mass ratio (q about 0.13) and a high inclination angle for this system. Two new long-period eclipsing binaries, GSC 814-323 and HD75638 (non-members of M67) were discovered. We also present ground-based DDO spectroscopy of ES Cnc and of the newly found eclipsing binaries. Especially interesting is HD75638, a member of a visual binary, which must itself be a triple or a higher-multiplicity system. New light curves of two delta Scuti pulsators, EX Cnc and EW Cnc, have been analyzed leading to detection of 26 and 8 pulsation frequencies of high temporal stability. Comment: accepted to MNRAS, 2008 August 28
09/2008;
