Hot Stars as Targets for Intensity Interferometry. Hannes Jensen Lund Observatory, Sweden

Transcription

1 Hot Stars as Targets for Intensity Interferometry Hannes Jensen Lund Observatory, Sweden

2 Aims Given recent progress in phase interferometry: which should be the prime observational targets for II? What is least difficult to observe? Starting point for observing programs, white papers, etc.

3 Selection Criteria What makes a target suitable for II? Bright High above background noise level, moonlight etc. Hot S/N improves greatly with target temperature Astronomically interesting Features on a (sub)milliarcsecond level. Deformation due to rapid rotation, pulsation, disks, winds, etc.

4 The Bright Star Catalogue The Bright Star Catalogue contains the ~9000 brightest stars.

5 Temperatures Effective temperatures were approximated with a polynomial fit to values from [Bessel et al, 1998, A&A333]. ~2600 objects are hotter than 9000 K and brighter than V=7

6 Final selection 34 stars exist with (Teff > 9000 K V < 2) Teff > K A few other interesting objects were added Angular diameters from the CHARM2 compilation. [Richichi et al., 2005, A&A431, 773]

7 Selected objects Temperature vs. apparent magnitude of selected stars. Circle size indicates angular diameter where available. 1 mas

8 List of Objects Name Angular size (mas) Rot. vel. * [km/s] Spec. class Teff [K] V [mag] Notes Achernar, HR B3Ve High rotational velocity, Be-star Rigel, HR B8Iab Emission line star, SN candidate Lambda Lep, HR B0.5IV Bellatrix, HR B2III Variable star Elnath, HR B7III Star in double system HR B0V Variable star HR B0.5V Star in double system Alnilam A, HR B0Iab Emission line star HR O9.5V High rotational velocity Beta CMa B1II/III Short period beta Cep variable Alhena, HR A0IV Star in double system S Mon, HR O7Ve Sirius, HR A1V Bright, well studied, high angular size EZ CMa, HR 2583? WN Highly variable W-R star Adara, HR B2Iab Star in double system Naos, HR O5Ia BY Dra variable, high rot. vel. HR WCv Double or multiple star HR A2IV * vrot sin i

9 List of Objects, contd. Name Angular size (mas) Rot. vel. [km/ s] Spec. class Teff [K] V [mag] Notes Beta Cen, HR B1III Beta Cep variable Tau Sco, HR B0.2V Lambda Sco, HR B2IV Beta Cep variable Kaus Austr., HR B9.5III Star in double system Vega, HR ? A0V Bright, well studied Peacock, HR B2IV Spectroscopic binary Deneb, HR A2Iae Alpha Cyg variable HR B6V High rotational velocity Fomalhaut, HR A4V First optically imaged exo-planet Eta Car, HR (CSS)? pec Highly unstable, SN candidate? WD ? Hottest WD known Gamma Vel, HR WC8+O9I 1.8 WR-O binary Regulus, HR B7V High rotational velocity Acrux, HR B0.5IV Spectroscopic binary HR B1V High rotational velocity Beta Cru, HR B0.5IV Beta Cep variable Eps UMa, HR A0p Variable star Spica, HR B1III-IV High rotational velocity, variable Alcaid, HR 5191 < B3V High rotational velocity, variable

10 Selected objects

11 Achernar (B3Ve) Very rapidly rotating Be-star Highly deformed due to rotation, observed with VLTI [de Souza et al., 2003, A&A407, 47] Teff K V [mag] 0.46 v sin i 250 km/s θ 1.85 mas Complex stellar winds due to rotation [e.g., Kervella et al., 2008] Circumstellar disk may be studied with II in its Hα emission Companion star suggested [Kervella & de Souza, 2007, A&A474, 49] [Kanaan et al., 2008, A&A, 486]

12 Rigel (B8Iab) The nearest blue supergiant Nearest type II supernova progenitor? [Stewart et al., 2009] Teff K V [mag] 0.12 v sin i 30 km/s θ 2.4 mas Periodic oscillations on many timescales [Stewart et al., 2009] Variation in absorption/emission in Hα lines [Morrison et al., 2009]

13 β Centauri (B1III) Teff K* The brightest β Cep variable Oscillations, line profile variations Highly complex spectroscopic binary, both components variable [Ausseloos et al., 2006, A&A455] V [mag] 0.61 v sin i θ 140 km/s 0.9 mas *both components approx. equal mass and temp. A challenge for current evolution scenarios in close binaries [Ausseloos et al., 2002 A&A209] Orbits measured with Sydney University Stellar Interferometer (SUSI) [Davis et al, 2005,MNRAS ]

14 Vega (A0 V) Widely studied standard star. Arguably the second most important star in the sky after the Sun [Gulliver et al., 94, ApJ429] Teff K V [mag] 0.03 v sin i 15 km/s θ 3.2 mas Realized to be a rapidly rotating pole-on star Center-limb intensities: 18x drop at 500 nm, compared to 5x drop for non-rotating model [Peterson et al., 2006, Nature 440, 896]

15 Fomalhaut (A4V) Host star of an optically imaged exoplanet Debris disk with planet(s) Teff K V [mag] 1.16 v sin i 100 km/s θ 2 mas

16 η Carinae Most luminous star known in the Galaxy Highly unstable, doomed to explode within years Imaged with HST and VLT to some 0.1 arcsec; Teff K V [mag] 6.21 v sin i? θ 5 mas* * Circumstellar shell VLTI data to milliarcsecond level shows asymmetries in winds due to rapid rotation [Weigelt et al., 2007, A&A, 464, 87] Images: eso.org

17 γ 2 Velorum (WC8+O9I) Closest and brightest Wolf-Rayet star. WR-O binary, important for understanding stellar evolution [North et al., 2007, MNRAS 377] Teff K V [mag] 1.8 v sin i? θ 0.4 mas Excellent system for studying massive stars and their interacting winds [Millour et al., 2007, A&A464] Already observed at Narrabri by Hanbury Brown et al.: Angular size in C III-IV emission at 465 nm shows stellar envelope five times larger than stellar disk in the continuum

18 Conclusions Observationally suitable and exciting targets exist all over the sky Much to be gained from sub-milliarcsecond measurements - way more than just stellar diameters!