Southern Massive Stars at High Angular Resolution Frank Tramper Hugues Sana (KU Leuven), Alex de Koter (University of Amsterdam) Introduction - Massive stars

• Rare and short-lived, but key players in the Universe

• Strong impact on their surroundings • Dominant sources of momentum (stellar winds and SNe) • Strong ionizing radiation • May halt or start star formation • Chemical enrichment: main producers of alpha-elements (CNO) • Re-ionization of the Universe

• Single-star evolution dominated by: • Mass-loss Metallicity • Rotation }

2 Massive star evolution 106.5 120 M 85 M WNh 6 60 M 10

40 M 5.5 Eta Carinae 10 25 M cWR 20 M 105 OB stars

Zero-Age Main Sequence 15 M RSG Antares 104.5 12 M Luminosity (solar units)

4 10 9M

WR124 103.5 100 000 30 000 10 000 5 000 3 000

Surface temperature (K) 3 But… binaries!

• Interactions dominate massive star evolution: 71% of all stars born as O-type will interact during their lifetime (Sana+ 2012).

Sana+ 2012 de Mink+ 2014

4 Binary detection

• Spectroscopy: short-period binaries through radial velocity variations • Traces separations up to ~1 AU • Provides minimal masses, and if inclination is known, absolute masses • Direct imaging: long-period binaries • Traces separations > 1000 AU for nearby stars

• Separation range between 1-1000 AU remains mostly unexplored

WR21a, Tramper+ 2016

5 Smash+: Southern Massive Stars at High Angular Resolution

• Target: all Southern O-type stars brighter than H=7 mag • Large programme (33 nights, PI Sana) on two VLT(i) instruments (Sana+ 2014) • Pioneer (117 stars): ~1-45 mas • NACO/SAM (162 stars): ~30-300 mas • Simultaneous AO corrected image: ~300-8000 mas • 96 stars with both

6 Smash+: Results

• 288 detected companions • Binary fraction including SBs (without bias correction!): • 91% within 8” • 100% of the dwarfs within 30 mas • On average: 2.3 companions The Astrophysical Journal Supplement Series,215:15(35pp),2014November Sana et al.

Figure 4. Examples of NACO data sets featuring the multiple systems HD 93129, HD 93206, HD 168075, and HD 319718. Only the central 5′′ 5′′ of the NACO FOV are shown. The faint E components of HD 93129 and HD 93206 are not visible with the adopted cut but their positions are marked. × (A color version of this figure is available in the online journal.) 7 the obtained χ 2 to decide which model fits best. The analysis of underlying idea is to test whether an observationSana+ is compatible 2014 the NACO data is split in two parts, according to the separation with that of a single star model. The main differences with Absil regime considered. At small working angles (ρ ! 250 mas, et al. are as follows. NACO/SAM), i.e., within the diffraction pattern of the NACO 1. We do not re-normalize the χ 2 with the best-fit binary PSF, we perform an interferometric analysis of the Fizeau in- model. This is because of the limited size of the data set terference pattern produced by the aperture mask to search for obtained for each individual object (typically two OBs). companions in Fourier space (Section 3.2). At larger working 2. The analysis is performed using the phase closures and the angles (ρ " 250 mas, NACO FOV), i.e., outside the object PSF, squared visibilities jointly. we use a cross-correlation technique to search for (mostly faint) 3. The stellar surfaces are considered to be unresolved, which companions in a 8′′ radius from the central object (Section 3.3). is a realistic assumption for our early-type objects observed with 100 m baselines. 3.1. PIONIER Data Analysis Consequently, in our analysis, the probability P1 for the data to be compatible with the single-star model is: The calibrated interferometric data were analyzed following 2 the approach detailed in Section 3.2 of Absil et al. (2011). The P1 1 CDFν (χ )(4) = − 9 Distance determination

• Known: apparent magnitude (H-band) • Needed: absolute magnitude (H-band)

• Use Martins & Plez 2006 synthetic photometry to derive relations as a function of spectral type (SpT) and luminosity class (LC). • Apparent magnitude corrected for close companions & extinction • Rayleigh-jeans domain: H - K = -0.10 for all SpT and LC

8 Distance determination - Check

• Resolved SB2’s with known spectral types

9 Mass determination

• Mass needed for both primaries (known SpT and LC) and companions (known H- band magnitude) • Derive relations for H-band bolometric correction as function of H-band magnitude for each LC • For LC I: use relation as function of SpT • Derive relation for exponent of mass-luminosity relation: L = Mx • Companions assumed to be dwarfs, unless this gives q > 1

10 Mass determination - Check

• SB2’s with known inclination: known primary mass

11 Results

• For separations < ~100 AU mass ratios and separations uniformly spread • Distribution of O-star companion masses compatible with Saltpeter IMF • Lack of massive companions above 100 AU

Tramper+ in prep. 12 What’s next: Going down to solar mass companions

13 What’s next: Going down to solar mass companions

PIONIER SAM NACO PIONIER, SAM, NACO : existing observations with the 1st generation VLT/VLTI instruments (Sana et al., ApJS 2014)

SPHERE, GRAVITY : detection limits of the 2sd generation VLT/ VLTI instruments (this proposal).

light gray : probability of background GRAVITY SPHERE or foreground contaminent >1%.

dark gray : probability of background or foreground contaminent >50%.

0.001 0.01 0.1 1 10 Angular Separation (“)

Fig. 7.— Plot of the magnitude di↵erence ( mag) vs. angular separations (⇢) for the detected pairs. Only one detection per object has been considered, and the H-band has been preferred whenever HDE303304available. The solid lines indicate the median H-band sensitivity ofWR25 our survey across the di↵erent separation ranges. The Ks sensitivity curves are similar. Di↵erent colors indicate observations with di↵erent instrumental configurations (PIONIER: blue, NACO/SAM: green, NACO FOV: red) while di↵erent symbols indicate di↵erent observational bands (H:filled,Ks: open). Large circles indicate objects detected by both SAM and PIONIER.

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14 Summary

• Most (if not all) massive stars are in a multiple system • The majority will interact during their lifetime

• The smash+ survey filled the gap between spectroscopy and direct imaging • 288 companions detected, mostly unknown • No distant massive companions

• Ongoing observations will go down to solar mass companions

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