Publications by Tony Lynas-Gray


Surveys with small optical telescopes

Astronomy and Geophysics Oxford University Press 60 (2019) 6.14–6.18-

A Lynas-Gray


A-Type Stars as a Unique Challenge in Time-Domain Studies

Proceedings of the International Astronomical Union Symposia and Colloquia Cambridge University Press 14 (2019) 230-235
Part of a series from Southern Horizons in Time-Domain Astronomy

A Lynas-Gray, G Mathys


New hot subdwarf variables from the EC survey

Monthly Notices of the Royal Astronomical Society Oxford University Press (2019)

D Kilkenny, HL Worters, A Lynas-Gray

© 2019 The Author(s). We present new results for hot subdwarf stars from the Edinburgh-Cape (EC) blue object survey. EC 03089-6421, an sdO star recently discovered to be a very rapid pulsator with periods near 31.1 and 34.2 s (29.2 and 32.1 mHz), is shown to have an even faster pulsation near 26.6 s (37.6 mHz) although all pulsations are variable in amplitude and effectively disappear in one of our runs. Five stars are discovered to be of the rapidly-pulsating (sdBV r ) type: EC 01441-6605, EC 10834-1301, EC 11275-2504, EC 11545-1459, and EC 21281-5010 each exhibit between one and three variations in the range 2-3 min (∼8.2-6.4 mHz) and are therefore p-mode pulsators. EC 15061-1442 shows a large-amplitude variation with a period ∼0.075 d if the star is a reflection effect binary and 0.15 d if an ellipsoidal variable. No eclipses are detected. Low-resolution EC survey classification spectroscopy is combined with published photometry from GALEX, WISE, and 2MASS and parallaxes from GAIA to derive, where possible, fundamental stellar parameters. The sdBV r stars have T eff in the range 34 000-45 000 K and log g between 5.0 and 5.6 consistent with p-mode pulsators. Derived stellar masses and radii are in the ranges 0.15-0.4 M ⊙ and 0.15-0.2 R⊙. The sdOV star, EC 03089-6421 is found to have T eff = 52 000 ± 3000 K and log g = 5.6 ± 0.2, and with a mass ∼0.1 M o could be a progenitor to an extremely low-mass white dwarf.


New hot subdwarf variables from the EC survey

Monthly Notices of the Royal Astronomical Society Oxford University Press 485 (2019) 4330–4342-

D Kilkenny, H Worters, A Lynas-Gray

We present new results for hot subdwarf stars from the Edinburgh-Cape (EC) blue object survey. EC 03089–6421, an sdO star recently discovered to be a very rapid pulsator with periods near 31.1 and 34.2 s (29.2 and 32.1 mHz), is shown to have an even faster pulsation near 26.6 s (37.6 mHz) although all pulsations are variable in amplitude and effectively disappear in one of our runs. Five stars are discovered to be of the rapidly-pulsating (sdBVr) type: EC 01441–6605, EC 10834–1301, EC 11275–2504, EC 11545–1459, and EC 21281– 5010 each exhibit between one and three variations in the range 2–3 min (∼8.2–6.4 mHz) and are therefore p-mode pulsators. EC 15061–1442 shows a large-amplitude variation with a period ∼0.075 d if the star is a reflection effect binary and 0.15 d if an ellipsoidal variable. No eclipses are detected. Low-resolution EC survey classification spectroscopy is combined with published photometry from GALEX, WISE, and 2MASS and parallaxes from GAIA to derive, where possible, fundamental stellar parameters. The sdBVr stars have Teff in the range 34 000–45 000 K and log g between 5.0 and 5.6 consistent with p-mode pulsators. Derived stellar masses and radii are in the ranges 0.15–0.4 M and 0.15–0.2 R. The sdOV star, EC 03089–6421 is found to have Teff = 52 000 ± 3000 K and log g = 5.6 ± 0.2, and with a mass ∼0.1 M could be a progenitor to an extremely low-mass white dwarf.


Orbital characteristics of the subdwarf-B and F V star binary EC 20117-4014(=V4640 SGR)

Astrophysical Journal American Astronomical Society 859 (2018) 145

T Otani, TD Oswalt, A Lynas-Gray, D Kilkenny, C Koen, M Amaral, R Jordan

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC 20117-4014 (=V4640 Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O’Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system’s precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3σ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was P˙ = 5.4 (±0.7) × 10−14 d d−1 , which shows that the sdB is just before the end of the core helium-burning phase.


Photometry and spectroscopy of the new sdBV CS 1246

Monthly Notices of the Royal Astronomical Society 403 (2010) 324-334

BN Barlow, BH Dunlap, JC Clemens, AE Lynas-Gray, KM Ivarsen, AP LaCluyze, DE Reichart, JB Haislip, MC Nysewander

We report the discovery of a large-amplitude oscillation in the hot subdwarf B star CS 1246 and present multicolour photometry and time-resolved spectroscopy supporting this discovery.We used the 0.41-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes array to acquire data in the u', g', r' and i' filters simultaneously over three consecutive nights in 2009 April. These data reveal a single oscillation mode with a period of 371.707 ± 0.002 s and an amplitude dependent upon wavelength, with a value of 34.5 ± 1.6 mma in the u' filter. We detected no additional frequencies in any of the light curves. Subsequently, we used the 4.1-m SOAR telescope to acquire a time-series of 248 low-resolution spectra spanning 6 h to look for line profile variations. Models fits to the spectra give mean atmospheric values of T eff = 28 450 ± 700K and log g = 5.46 ± 0.11 undergoing variations with semi-amplitudes of 507 ± 55K and 0.034 ± 0.009, respectively. We also detect a radial velocity oscillation with an amplitude of 8.8 ± 1.1 kms-1. The relationship between the angular and physical radii variations shows that the oscillation is consistent with a radial mode. Under the assumption of a radial pulsation, we compute the stellar distance, radius and mass as d = 460 ± 19090 pc, R = 0.19 ± 0.08 R⊙ and M = 0.39 ± 0.300.13M⊙, respectively, using the Baade-Wesselink method. © 2010 The Authors. Journal compilation © 2010 RAS.


The rapidly pulsating sdO star, SDSS J160043.6+074802.9

Monthly Notices of the Royal Astronomical Society 401 (2010) 23-34

C Rodríguez-López, AE Lynas-Gray, D Kilkenny, J MacDonald, A Moya, C Koen, PA Woudt, DJ Wium, B Oruru, E Zietsman

A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields Teff = 70 000 ± 5000 K and log g = 5.25 ± 0.30, together with a most likely type of K3 V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. Therefore, it seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range. © 2009 RAS.


Detection of photometric variations in the sdBV star jl 166

Astronomical Journal 138 (2009) 686-690

BN Barlow, BH Dunlap, AE Lynas-Gray, JC Clemens

We report the discovery of oscillations in the hot subdwarf B (sdB) star JL 166 from time-series photometry using the Goodman Spectrograph on the 4.1 m Southern Astrophysical Research Telescope. Previous spectroscopic and photometric observations place the star near the hot end of the empirical sdB instability strip and imply the presence of a cool companion. Amplitude spectra of the stellar light curve reveal at least 10 independent pulsation modes with periods ranging from 97 to 178 s and amplitudes from 0.9 to 4 mma. We adopt atmospheric parameters of T eff= 34,350 K and log g = 5.75 from a model atmosphere analysis of our time-averaged, medium-resolution spectrum. © 2009. The American Astronomical Society.


A new ab initio ground-state dipole moment surface for the water molecule

JOURNAL OF CHEMICAL PHYSICS 128 (2008) ARTN 044304

L Lodi, RN Tolchenov, J Tennyson, AE Lynas-Gray, SV Shirin, NF Zobov, OL Polyansky, AG Csaszar, JNP van Stralen, L Visscher