arXiv subjects

A. W. Shafter

Publications and source records attributed to A. W. Shafter.

41 records · Page 3Linked to original sources

arXiv2008

Time-Resolved Photometry of the Optical Counterpart of Swift J2319.4+2619

Time-resolved CCD photometry is presented of the V~17 optical counterpart of the newly-discovered, hard-X-ray-emitting polar Swift J2619.4+2619. A total of ~20 hr of data obtained over five nights in various bandpasses (B, V, R, and I) reveals a strong quasi-sinusoidal modulation in the light curve at a best-fitting period of 0.1254 d (3.01 hr), which we associate with the orbital period of the system (one-day aliases of this period at 0.1114 d and 0.1435 d are considered, but appear to be ruled out by our analysis). The amplitude of the modulation increases with wavelength from ~0.8 mag in B to ~1.1 mag in R and I. The increase in amplitude with wavelength is typical of polar systems where the modulated radiation comes from cyclotron emission. The combination of the relatively long orbital period and the emission of hard X-rays suggest that Swift J2619.4+2619 may be a good candidate for an asynchronous polar system.

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arXiv2007

M31N-2007-06b: A Nova in the M31 Globular Cluster Bol 111

We report spectroscopic observations of the nova M31N-2007-06b, which was found to be spatially coincident with the M31 globular cluster Bol 111. This nova is the first out of more than 700 discovered in M31 over the past century to be associated with one of the galaxy's globular clusters. A total of three spectra of the nova were obtained 3, 6, and 36 days post discovery. The data reveal broad (FWHM ~3000 km/s) Balmer, NII, and NIII emission lines, and show that the nova belongs to the He/N spectroscopic class. The He/N class of novae are relatively rare, making up roughly 15% of the novae with measured spectra in M31, and roughly 20-25% of the Galactic novae for which spectroscopic data are available. The implications of a nova, particularly an He/N nova, occurring in a globular cluster are discussed.

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arXiv2007

Photometry of VS0329+1250: A New, Short-Period SU Ursae Majoris Star

Time-resolved CCD photometry is presented of the recently-discovered (V~15 at maximum light) eruptive variable star in Taurus, which we dub VS0329+1250. A total of ~20 hr of data obtained over six nights reveals superhumps in the light curves, confirming the star as a member of the SU UMa class of dwarf novae. The superhumps recur with a mean period of 0.053394(7) days (76.89 min), which represents the shortest superhump period known in a classical SU UMa star. A quadratic fit to the timings of superhump maxima reveals that the superhump period was increasing at a rate given by dP/dt ~ (2.1 +/- 0.8) x 10^{-5} over the course of our observations. An empirical relation between orbital period and the absolute visual magnitude of dwarf novae at maximum light, suggests that VS0329+1250 lies at a distance of ~1.2 +/- 0.2 kpc.

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arXiv2006

Modeling Eclipses of the Novalike Variable TT Triangulum

Multicolor (BVRI) light curves of the eclipsing novalike variable TT Tri are presented and analyzed with a parameter-fitting eclipse model. The mass ratio of TT Tri is poorly constrained, but must lie roughly in the range 0.3 >R_1) generally resulted in a higher white dwarf temperature, and a steepening of the disk temperature profile, but were not required to achieve a viable steady-state disk solution. No evidence was found for a luminous bright spot in the system, which is not surprising given the lack of a pre-eclipse "hump" in the light curve. A total of 22 eclipse timings were measured for the system, which yielded an ephemeris for the times of mid-eclipse given by HJD = 2,453,618.953(3) + 0.1396369(4) E. A comparison of the observed brightness and color at mid-eclipse with the photometric properties of the best-fitting model suggests that TT Tri lies at a distance of ~400-500 pc. (abstract abridged)

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arXiv2006

Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim

Multicolor (BVRI) light curves of the eclipsing classical nova V Per are presented, and a total of twelve new eclipse timings are measured for the system. When combined with previous eclipse timings from the literature, these timings yield a revised ephemeris for the times of mid-eclipse given by HJD = 2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a parameter-fitting model that assumes four sources of luminosity: a white dwarf primary star, a main-sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass-transfer stream and the disk periphery. A matrix of model solutions are computed, covering an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors. For models that treat the accretion disk as a flat structure without a rim, optimum fits require that the disk have a flat temperature profile. Although models with a truncated inner disk (R_in >> R_wd) result in a steeper temperature profile, steady-state models with a temperature profile characterized by T(r) \propto r^{-3/4} are found only for models with a significant disk rim. A comparison of the observed brightness and color at mid-eclipse with the photometric properties of the best-fitting model suggests that V Per lies at a distance of ~ 1 kpc.

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