The variable nature of the OB star HD13831 Dr. Amira Val Baker Celebrating Ten Years of Science with STELLA Wednesday 9th November 2016
STELLA robotic telescope Dr Ana Gonzales-Galan Celebrating Ten Years of Science with STELLA Wednesday 9 th November 2016
Observational astrophysics how systems change with time Quasars Cepheids Celebrating Ten Years of Science with STELLA Wednesday 9 th November 2016 Accretion disks
Time analysis Infer nature of astrophysical object: What is it? What is the source of its variable nature? How was it formed? How is it evolving? Predictions new physics Extremely important Robotic telescopes allow data collection
The variable nature of the OB star HD13831 Dr Amira Val Baker Celebrating Ten Years of Science with STELLA Wednesday 9th November 2016
HD 13831 (V473Per) OB star unstable Located in double cluster h and X Persei Originally photometric constant (Hill 1967) Periodic variations (0.03 magnitudes) in U, V and B bands over 4.6 hr cycle (Garrido & Delgado 1982) B0.5 IV Beta Cephei star
HD 13831 Variable nature confirmed (De cat et al. 2007; Lefevre et al. 2009) B0 IIIp p = broad spectral lines & HeII 4686 in emission Hα in emission Be star (Kohoutek & Wehmeyer, 1999) Be star Binary system Variable Hα and He II 4686 Be binary star
Observations High resolution spectroscopy - 1.2 m STELLA robotic telescope STELLA Echelle Spectrograph (SES) 0.4 A o /pixel 3870 8820 A o 19 spectra over 6 month period 5 th September 2013 15 th March 2014 Reduced via standard pipeline procedures H, He, Fe III, Si III, N II, O II, Ca II B0 III Hα, He II 4686 in emission Be star
Hα and HeII 4686
Spectral Analysis Spectral profile fitting Gaussian fits to spectral lines - IDL peak intensity, line centre, FWHM Radial velocities Doppler shifts ΔλΤ λ = v Τc He, DIBs Balmer lines excluded likely contaminated by stellar wind Heliocentric corrected RV v Heliocentric Julian Date
Spectral Analysis Stability of observations / accurate Wavelength calibration DIBs repeatability of apparent strength invariant HRV - Linear correlation with <10% variance Period analysis a periodogram with PERIOD (Starlink) epoch folding analysis around this preliminary value Period ~ 70.76 days
DIBs 5889 RV vs HJD
He I 5876 HRV vs phase (P=70.76 days)
Hα V/R vs phase P=70.76 days
Analysis v/r variability V R peak separation Δv R d = GM v 2 = GM sin 2 i ( 1 2 Δv)2 = 4 6.5 R V/R ratio disc dynamics V/R v phase shows Significant variability global on-armed density wave (Okazaki, 1991) disc sufficiently stable (Hanuschik, 1995) Be star in a binary system
Hα V/R vs phase P=70.76 days
Conclusions 1. Periodicity period 70.76 days likely orbital period no presence of second star invisible companion likely associated with ROSAT source 1RXS J021639.3+564406 2. Emission lines Be star variability sufficiently stable for global one-armed density waves indicative of Be / X ray binary
Summary Time-analysis astrophysics is important to our understanding of the dynamics of the Universe Studied the varying line profiles of HD 13831 - wavelength shifts - profile shapes Concluded that HD 13831 is likely part of a binary system consisting of a Be star and the X-ray source 1RXS J021639.3+564406 Future observations Optical and X-ray would help confirm the nature of this intriguing star!