Statement of the problem and programmatic implications for N ASA Bertrand Mennesson JPL May 20 2015 Outline Brief Review of Observational evidence over the last 10 years Ancillary measurements and ID: 810731
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Slide1
Hot Excess around Main Sequence Stars: Statement of the “problem” and programmatic implications for NASA
Bertrand Mennesson, JPL
May 20, 2015
Slide2OutlineBrief Review of Observational evidence over the last 10 yearsAncillary measurements and basic constraints on origin of measured excesses
How problematic is it for future
exo
-Earth direct imaging missions?
Slide3History of “NIR” (lIR < 5m
m
) excesses detected around “old” MS stars
2006:
t
he “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 …)
Slide4Where does the excess come from?Basic constraints: CHARA/FLUOR FoV = 0.5” FWHM, VLTI/PIONIER = 0.2” FWHMV=Vs
.(1-f) +
f.Vd
r
esolved excess detectable as close as 5mas with CHARA 34m baseline at 2.2 mm
Case of 1% excess around unresolved startau Cet G8V4.7 Rstar10 TauF9V8.7eta LepF1V9.2lam Gem
A3V
11.3
bet LeoA3V
7.0
ksi BooG8V
7.9
Altair
A7V
2.8
VegaA0V
2.8
110 Her
F6V
9.6
Zet
Aql
A0V
11.0
alf
Cep
A7IV
6.0
Slide5Where does the excess come from?Palomar Fiber Nuller (3.4m, 2.2mm) limits on Vega (<0.2AU, or >2AU, or time variable)
Lower quality PFN observations of
l
Gem,
t
Cet
, x Boo, Altair and b Leo show no NIR excess detected at ~1% (3s) upper limitBulk of NIR Excess must reside inside of 20 mas or outside of 200 mas
Slide6Weak excess counterpart at 10 mm (if any)KIN can detect CS dust emission at 1% level btw 5mas and 200 mas,
most
sensitive at 8.5
m
m
Out of 4 stars with
ONLY a NIR excess, NONE show a MIR excess with KINOut of 11 NIR excess stars observed by KIN:Only two show a significant MIR excess: b Leo and Fomalhaut. Both have a FIR excess2 more close to the detection limit: Altair and Vega (candidate excesses)None of the FGK NIR excess stars show a MIR excessIf NIR excess due to dust grains, they must somehow elude detection at MIR wavelengthsDoes that really necessarily imply small (<~ 1 mm) dust grains??KIN paper result: conversely to FIR excesses, NIR excesses do NOT correlate with MIR excessesPointing to a different origin?At least at the KIN sensitivity limit LBTI may change this picture
Slide7NIR 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 …
I
s
it
the exception or the
rule?
Best radiative transfer fit (Jeremy)
points to 2 distinct dust populations: - Some <0.5 mm 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 NIRThe 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
Slide8Basic Problems and QuestionsSuch small dust particles should be expelled by RP in very short timescales (?)But NIR excess is observed around many starsDust must either be replenished quasi continuouslyIs there enough supply for that? Or trapped in the inner region
How?
Alternative scenarios? Is it really dust?
Slide9Programmatic 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
Slide10What 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 zodisA 1% NIR excess flux coming from a Sun-like zodi distribution corresponds to > 1000 zodis !1 Zodi 5 Zodis10 Zodis20 Zodi 50 Zodis100 Zodis
Slide11How 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?
S
o 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?
Slide12Back-up
Slide13History of excesses detected at lIR < 5m
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 stars2014: VLTI – PIONIER H initial survey finds 9 more out of 85 targets
Slide14Dispersion 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/dl), i.e a period of 1/(B* dn_air/dl) in theta for small ZA. Effect increases with Dl and BLarger B means faster variations calling for closer cals FLUOR S1-S2 300nm BWFLUOR S1-S2 200nm BWPFN 3.4m200nm BW
Slide15History of “NIR” (lIR < 5m
m
) excesses detected around “old” MS stars
2006:
t
he “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)