1. Hot Excess around Main Sequence Stars: Statement of the “problem” and programmatic implications for NASA Bertrand Mennesson, JPL May 20, 2015

2. Outline Brief Review of Observational evidence over the last 10 years Ancillary measurements and basic constraints on origin of measured excesses How problematic is it for future exo-Earth direct imaging missions?

3. History of “NIR” ( IR  < 5  m ) excesses detected around “old” MS stars 2006: the “Vega surprise” at CHARA (Absil et al 2004) (earlier hints of an excess at PTI, Ciardi et al. 2001) 2007 - 2009: other stars show it too (DiFolco et al. 2007, Absil et al. 2008, Akeson et al. 2009) 2009-2010: other interferometers see it (Absil et al. 2009, Defrere et al. 2012) 2011: coronagraphs see predicted companions (Mawet et al. 2011) 2011-12: first spectroscopic detections of very hot excesses (Lisse et al. 2012, Weinberger et al. 2011) 2013: CHARA initial survey of 40 single MS stars says it is fairly common (11/40)! (Absil et al. 2013) 2014: larger VLTI dispersed H-band survey sees it too, but less often (9/85) (Ertel et al. 2014) > 2014: on-going efforts to expand NIR interferometric and spectroscopic surveys (Steve, Nic, Paul, Gene, Casey …)

4. Where does the excess come from? Basic constraints: – CHARA/FLUOR FoV = 0.5” FWHM, VLTI/PIONIER = 0.2” FWHM – V=V s.(1-f) + f.V d  resolved excess detectable as close as 5mas with CHARA 34m baseline at 2.2  m Case of 1% excess around unresolved star tau Cet G8V 4.7 Rstar 10 Tau F9V 8.7 eta Lep F1V 9.2 lam Gem A3V 11.3 bet Leo A3V 7.0 ksi Boo G8V 7.9 Altair A7V 2.8 Vega A0V 2.8 110 Her F6V 9.6 Zet Aql A0V 11.0 alf Cep A7IV 6.0

5. Where does the excess come from? Palomar Fiber Nuller (3.4m, 2.2  m) limits on Vega ( 2AU, or time variable) Lower quality PFN observations of Gem,  Cet,  Boo, Altair and  Leo show no NIR excess detected at ~1% (3  ) upper limit – Bulk of NIR Excess must reside inside of 20 mas or outside of 200 mas

6. Weak excess counterpart at 10  m (if any) KIN can detect CS dust emission at 1% level btw 5mas and 200 mas, most sensitive at 8.5  m Out of 4 stars with ONLY a NIR excess, NONE show a MIR excess with KIN Out of 11 NIR excess stars observed by KIN: – Only two show a significant MIR excess:  Leo and Fomalhaut. Both have a FIR excess – 2 more close to the detection limit: Altair and Vega (candidate excesses) – None of the FGK NIR excess stars show a MIR excess If NIR excess due to dust grains, they must somehow elude detection at MIR wavelengths – Does that really necessarily imply small (<~ 1  m) dust grains?? KIN paper result: conversely to FIR excesses, NIR excesses do NOT correlate with MIR excesses – Pointing to a different origin? At least at the KIN sensitivity limit  LBTI may change this picture

7. NIR excess may be the “tip of the iceberg” pointing to a dimmer MIR dust population located further out (LBTI to say?) The case of Fomalhaut … – Is it the exception or the rule? Best radiative transfer fit (Jeremy) points to 2 distinct dust populations: - Some <0.5  m unbound hot carbon dust grains confined btw 0.1 AU and 0.3 AU - Larger (bound) grains located at ~ 2AU, having a higher total mass but contributing a lower MIR excess than the small grains do in the NIR The small hot grains would be produced by disruption of the dimmer outer population and may act as a signpost of dust in the HZ? Fomalhaut NIR/MIR excess modeling Mennesson et al. 2013 & Lebreton et al. 2013

8. Basic Problems and Questions Such small dust particles should be expelled by RP in very short timescales (?) But NIR excess is observed around many stars Dust must either be replenished quasi continuously – Is there enough supply for that? Or trapped in the inner region – How? Alternative scenarios? Is it really dust?

9. Programmatic considerations NIR and MIR Exozodi Surveys are extremely relevant to inform future exo-Earth imaging missions Understanding the measured excess origin is key in order to properly assess programmatic impact

10. What is the impact of NIR excess on future exo-Earth imaging missions? Synthetic Coronagraphic (PIAA 4m) Visible Images for a Sun-Earth System located at 10 pc with 1,5,10,20,50 or 100 zodis (Defrere et al. 2012) Bright dust clumps may outshine planetary flux if exozodi level is larger than ~10 zodis A 1% NIR excess flux coming from a Sun-like zodi distribution corresponds to > 1000 zodis ! 1 Zodi 5 Zodis 10 Zodis 20 Zodi 50 Zodis 100 Zodis

11. How much of a problem is the NIR excess phenomenon for future exo-Earth imaging missions? Where is the NIR excess source located? – Measure its spatial brightness distribution in the NIR – Establish whether or not it comes from dust in the HZ What is its wavelength dependence? What is its stellar spectral type dependence? Is it thermal emission or scattering, or both? – So we can more easily extrapolate to the visible Are NIR surveys a mandatory complement to MIR surveys? If NIR excess not coming from HZ, can it still tell us about dust in the HZ?

12. Back-up

13. History of excesses detected at IR  < 5  m around “old” MS stars 2006: The Vega surprise at CHARA 2007 - 2009: Other stars show similar ~1% kBand excesses ! (T Cet, zet Aql, bet Leo, Zet lep) 2009-2010: Other interferometers see it (Vega: IOTA, a Psa: VLTI) 2011: Coronagraphs see expected companions (eps Cep) 2011-12: Spectroscopic detections of very hot excesses (Lisse eta crv, Weinberger BD +20 307) 2013: CHARA K initial survey finds 11 excess around 40 single MS stars 2014: VLTI – PIONIER H initial survey finds 9 more out of 85 targets

14. Dispersion Effects due to Atmospheric Refraction (ZA projected along baseline direction) - The phase at zero group delay (and hence the broad-band visibility) is ~ unchanged when geometric opd B.sin(theta) changes by 1/(dn_air/d ), i.e a period of 1/(B* dn_air/d ) in theta for small ZA. -Effect increases with  and B -Larger B means faster variations calling for closer cals FLUOR S1-S2 300nm BW FLUOR S1-S2 200nm BW PFN 3.4m 200nm BW

15. History of “NIR” ( IR  < 5  m ) excesses detected around “old” MS stars 2006: the “Vega surprise” at CHARA (Absil et al 2004) (after hints of an excess at PTI, Ciardi et al. 2001) 2007 - 2009: other stars show it too (DiFolco et al. 2007, Absil et al. 2008, Akeson et al. 2009) 2009-2010: other interferometers see it (Absil et al. 2009, Defrere et al. 2012) 2011: coronagraphs see predicted companions (Mawet et al. 2011) 2011-12: first spectroscopic detections of very hot excesses (Lisse et al. 2012, Weinberger et al. 2011) 2013: CHARA initial survey of 40 single MS stars says it is fairly common (11/40)! (Absil et al. 2013) 2014: larger VLTI dispersed H-band survey sees it too, but less often (9/85) (Ertel et al. 2014) > 2014: on-going efforts to expand NIR interferometric and spectroscopic surveys (Steve, Nic & Paul, Casey)