Transcript UV ENVIRONMENT OF EXOPLANETS

UV ENVIRONMENT OF EXOPLANETS
Jeffrey Linsky, Kevin France, and
Rachel Bushinsky
University of Colorado
Boulder Colorado
ExoClimes 2012
Aspen Colorado
15-20 Jan 2012
Simulated spectrum of GJ 436 (M2.5 V with a
0.073MJ exoplanet). Note emission lines and
photo-absorption cross-sections of H2O and CH4
COS spectrum of 2M1207 a young M8 brown dwarf with a
CS disk (H2) and accretion (C IV) but no Si III-IV or Mg II
emission lines (France et al. ApJ 715, 596 (2010))
HST/STIS spectrum of AU Mic (M1 V) (Pagano et al. ApJ
532, 497 (2000). What line emits most of the UV flux?
UV spectra of solar-mass stars
(spectral types G0-G2 dwarfs)
“Sun in time Project”. Fluxes at 1 AU from solar
type stars as a function of age (Ribas et al. ApJ
622, 680 (2005)). Flux is very sensitive to age
(activity) at shorter wavelengths.
Spectral flux (for solar type stars) decreases with
age most rapidly at the shortest wavelengths. Is
the same true for M dwarfs?
Reconstructing Lyman-α Line Profiles Using
Information on the Local ISM (Wood et al.
ApJS 159, 118 (2005).
Left: ξ Boo A (G8 V). Right: AD Leo
(M3.5 V) and AU Mic (M0 V).
Observed and reconstructed Lyman-α line
profiles (Wood et al. ApJS 159, 118 (2005)
Limitations on the Lyman-α line
reconstruction technique
• Must be able to resolve
the D I Lyman-α line to
reconstruct the H I line.
• Effective horizon at log
N(HI)=18.7 (15-100 pc).
• Should also have high
resolution spectra of
metal lines (e.g., MgII or
FeII) to determine
whether many velocity
components in the line
of sight.
Curves for increasing HI column
density are for log N(HI) = 17.5,
17.8, 18.1, 18.4, 18.7. Solid and
dashed lines are for T=10,000 and
5,000 K. (Wood et al. 2005)
Observed and reconstructed
Lyman-α flux for GJ667C (M1.5V)
2 exoplanets at 0.05 and 0.12 AU.
Solar Spectral Irradiance at Earth
(moderate activity)
Band
X-ray (ROSAT)
10-30Å
30-100Å
100-300Å
300-911Å
911-1027Å
Lyman-α
1200-1600Å
minus Ly-α
f(erg/cm2/s)
0.41
0.013
0.42
1.2
1.4
0.23
5.1
2.44
Range Factor
10
5
3
3
2
1.5
1.5
1.4
UV and X-ray flux emitted by AU
Mic (M1 V)
Spectral Region Obs. flux (10-12
erg/cm2/s)
Lyman-α
10.3
(1216Å)
(Reconstructed)
1175-1700Å
1.6
except Lyman-α (HST/STIS)
933-1176Å
0.75
(FUSE)
X-ray
36.1
(ROSAT)
Reference
Wood et al.
(2005)
Pagano et al.
(2000)
Redfield et al.
(2002)
Wood et al.
(2005)
HST observations of M dwarfs with exoplanets
(programs 12034, 12035, and 12464)
Star + exoplanets d(pc)
COS/FUV STIS/Lyα+
GJ436 M3.5V+1
10.14 2012 plan 2012 plan
GJ581 M5.0V+4
6.21
07/2011 ? 07/2011 ?
GJ667C M1.5V+2 6.95
09/2011
GJ832 M1.5V+1
4.95
2012 plan 07/2011
GJ876 M5.0V+4
4.69
01/2012
11/2011
GJ1214 M4.5V+1 12.95 2012 plan 2012 plan
Maps of n(HI) computed in hydrodynamic models
of stellar atmospheres (Wood et al 2005). Scales
are in AU. Solid line indicates LOS to the observer.
61 Vir has 3 exoplanets located inside of its hydrogen wall.
Interstellar, astrospheric, and
heliospheric Lyman-α absorption
• Interstellar gas flow from
above.
• Line of sight passes through
astrosphere, ISM, and then
heliosphere
• Astrospheric absorption is blue
compared to ISM because H
slows down in the astropause
as seen by the star.
• Heliospheric absorption is red
compared to ISM because H
slows down in the heliopause.
• Astrospheric absorption
proportional to stellar mass
loss rate.
Measuring stellar mass loss rates from the
astrospheric absorption feature on the blue
side of interstellar Lyman-α absorption
Mass loss rate vs activity (X-ray
surface flux) and stellar age
• Solid dots indicate dwarf
stars (Prox Cen and EV
Lac are only M dwarfs).
• Near Fx=106 there is a
break suggesting a
change in magnetic field
structure.
• More measurements are
needed (HST GO-19
proposal).
• Ṁ ~ FX1.34±0.18 ~ t2.33±0.55
Conclusions
• Stellar UV+FUV+EUV flux incident on an exoplanet’s
atmosphere photodissociates important molecules like
H2O and CH4 and photoionizes important atoms like H
and O.
• Reconstructed Lyman-α dominates the UV flux often by
a very large factor.
• Lyman-α and UV stellar fluxes for G stars follow a
regular dependence on B-V and rotation period (a proxy
for stellar activity).
• Lyman-α and UV fluxes of M stars cannot be easily
predicted and must be observed. We have HST
observing programs for M stars with exoplanets.
• We have found a scaling law for stellar mass loss rates
which important for computing charge exchange rates.
We have an HST/STIS observing program to extend this
to M dwarfs.
We are now writing HST
proposals for new observations
of M dwarfs with exoplanets
Those interested in providing data for
new targets or in theoretical analysis
(e.g., atmospheric chemistry
calculations) are welcome to join the
proposing team. Please see me.