The variable nature of the OB star HD13831 Dr. Amira Val Baker. Celebrating Ten Years of Science with STELLA Wednesday 9th November 2016

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1 The variable nature of the OB star HD13831 Dr. Amira Val Baker Celebrating Ten Years of Science with STELLA Wednesday 9th November 2016

2 STELLA robotic telescope Dr Ana Gonzales-Galan Celebrating Ten Years of Science with STELLA Wednesday 9 th November 2016

3 Observational astrophysics how systems change with time Quasars Cepheids Celebrating Ten Years of Science with STELLA Wednesday 9 th November 2016 Accretion disks

4 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

5 The variable nature of the OB star HD13831 Dr Amira Val Baker Celebrating Ten Years of Science with STELLA Wednesday 9th November 2016

6 HD (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

7 HD 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

8 Observations High resolution spectroscopy m STELLA robotic telescope STELLA Echelle Spectrograph (SES) 0.4 A o /pixel A o 19 spectra over 6 month period 5 th September 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

9 Hα and HeII 4686

10 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

11 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 ~ days

12 DIBs 5889 RV vs HJD

13 He I 5876 HRV vs phase (P=70.76 days)

14 Hα V/R vs phase P=70.76 days

15 Analysis v/r variability V R peak separation Δv R d = GM v 2 = GM sin 2 i ( 1 2 Δv)2 = 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

16 Hα V/R vs phase P=70.76 days

17 Conclusions 1. Periodicity period days likely orbital period no presence of second star invisible companion likely associated with ROSAT source 1RXS J Emission lines Be star variability sufficiently stable for global one-armed density waves indicative of Be / X ray binary

18 Summary Time-analysis astrophysics is important to our understanding of the dynamics of the Universe Studied the varying line profiles of HD wavelength shifts - profile shapes Concluded that HD is likely part of a binary system consisting of a Be star and the X-ray source 1RXS J Future observations Optical and X-ray would help confirm the nature of this intriguing star!