Observation and analysis of the new W -type W UMa eclipsing binary star VSX J053024.8+842243

2017 January 22

David Boyd

Summary

Using multicolour photometry we have confirmed the binary nature of the new W-type W UMa eclipsing binary star VSX J053024.8+842243 and established its primary eclipse ephemeris to be HJD= 2455924.38150(26) + 0.4322929(1) * E. Using the lightcurve modelling code PHOEBE and published data on the evolution of W-type contact binaries, we found the primary and secondary components to have masses 0.50M_¤ and 1.44M_¤, radii 0.87R_¤ and 1.42R_¤, luminosities 0.98L_¤ and 1.91L_¤, temperatures 6145K and 5702K and binary orbit inclination 59.4°. We found the distance to the binary to be 511 parsec, its E(B-V) colour excess 0.04 and its intrinsic (B-V) colour index 0.62. A low resolution spectrum corrected for interstellar reddening confirmed its spectral type as G2V.

Introduction

Sebastian Otero compiled a list of suspected eclipsing binary stars on the basis of survey observations.¹ One of the stars in his list, GSC 04621-00193 (=2MASS J05302483+8422431), is located in the constellation of Cepheus at RA 05h 30m 24.8s, Dec +84° 22′ 43″ (J2000). Its suspected orbital period was listed as 0.355 days. A search of survey databases revealed data on the star in The Amateur Sky Survey (TASS)² and the Northern Sky Variability Survey.³ The TASS data was noisy and revealed no clearly defined periods.

The NSVS data, recorded over a 20-week period in 1999, was of higher quality and a period search using Peranso⁴ gave a clearly defined period at 0.355 days, apparently confirming the suggested period. However these were small datasets of 92 and 82 observations respectively. Accurate and more extensive photometry would be necessary to verify the star’s true nature.

Photometric observations

V-band CCD photometry was carried out on 3 nights in 2011 December using a 0.35m SCT and SXVR-H9 CCD camera. This produced 1200 images. As this was a new variable not in any of the comparison star databases, suitable comparison stars had to be identified. Johnson B and V and Sloan g, r and i magnitudes for nearby stars were found from the AAVSO Photometric All-Sky Survey (APASS 2015)⁵ and conversion formulae from the Sloan Digital Sky Survey website⁶ were used to calculate Cousins Rc and Ic magnitudes. Five stars close to the variable were chosen as comparison stars. All images were dark-subtracted and flat-fielded and ensemble differential aperture photometry performed with respect to these five comparison stars to find V magnitudes for the variable.

Further observations using B, V, Rc and Ic filters were made on 5 nights in 2012 July and August and the derived magnitudes were transformed onto the standard photometric system using the procedure described in ref.7. Average magnitude uncertainties were 0.018 in B, 0.008 in V, 0.011 in Rc and 0.021 in Ic. Observations were obtained on two further nights in 2015 December and 2016 January to refine the orbital period. The times of all observations were converted to Heliocentric Julian Dates (HJD/UTC) to correct for the orbital motion of the Earth.  (continued)(Login or click above to view the fully illustrated article in PDF format)