J/A+A/650/A73 Synthetic XUV spectra of GJ 3470 (Bourrier+, 2021)
The Hubble PanCET program: long-term chromospheric evolution and flaring
activity of the M dwarf host GJ 3470.
Bourrier V., dos Santos L.A., Sanz-Forcada J., Garcia Munoz A., Henry G.W.,
Lavvas P., Lecavelier des Etangs A., Lopez-Morales M., Mikal-Evans T.,
Sing D.K., Wakeford H.R., Ehrenreich D.
<Astron. Astrophys. 650, A73 (2021)>
=2021A&A...650A..73B 2021A&A...650A..73B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Planets ; Spectra, ultraviolet
Keywords: planets and satellites: atmospheres - techniques: spectroscopic -
planet-star interactions -
planets and satellites: individual: GJ 3470 - stars: chromospheres
Abstract:
Neptune-size exoplanets seem particularly sensitive to atmospheric
evaporation, making it essential to characterize the stellar
high-energy radiation that drives this mechanism. This is particularly
important with M dwarfs, which emit a large and variable fraction of
their luminosity in the ultraviolet and can display strong flaring
behavior. The warm Neptune GJ 3470b, hosted by an M2 dwarf, was found
to harbor a giant exosphere of neutral hydrogen thanks to three
transits observed with the Hubble Space Telescope Imaging Spectrograph
(HST/STIS). Here we report on three additional transit observations
from the Panchromatic Comparative Exoplanet Treasury program, obtained
with the HST Cosmic Origin Spectrograph. These data confirm the
absorption signature from GJ 3470b's exosphere in the stellar
Lyman-α line and demonstrate its stability over time. No
planetary signatures are detected in other stellar lines, setting a
3σ limit on GJ 3470b's far-ultraviolet (FUV) radius at 1.3
times its Roche lobe radius. We detect three flares from GJ 3470. They
show different spectral energy distributions but peak consistently in
the SiIII line, which traces intermediate-temperature layers in the
transition region. These layers appear to play a particular role in
GJ 3470's activity as emission lines that form at lower or higher
temperatures than SiIII evolved differently over the long term.
Based on the measured emission lines, we derive synthetic X-ray and
extreme-ultraviolet (X+EUV, or XUV) spectra for the six observed
quiescent phases, covering one year, as well as for the three flaring
episodes. Our results suggest that most of GJ 3470's quiescent
high-energy emission comes from the EUV domain, with flares amplifying
the FUV emission more strongly. The neutral hydrogen photoionization
lifetimes and mass loss derived for GJ 3470b show little variation
over the epochs, in agreement with the stability of the exosphere.
Simulations informed by our XUV spectra are required to understand the
atmospheric structure and evolution of GJ 3470b and the role played by
evaporation in the formation of the hot-Neptune desert.
Description:
We provide ten tables that contain synthetic XUV spectra of the star
GJ 3470 at six different epochs (defined as visits A, B, C, D, E, F in
the paper). The suffix "quiescent" indicates the quiescent phases in
each epoch. The files ending with the suffix "flare" indicate the
flaring phases in visits E and F: two for the independent flares in
visit E, and two for the peak and decay phases of the flare in visit
F. The spectra extend up to 1600Å and are defined at 1au from the
star as a function of wavelength in the stellar rest frame. They are
derived from a model of the stellar atmosphere, informed by
measurements of X-ray emission from the stars GJ 3470 and AD Leo, and
by measurements of chromospheric/transition region lines from GJ 3470.
Objects:
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RA (2000) DE Designation(s)
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07 59 05.84 +15 23 29.2 GJ 3470 = LP 424-4
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 56 10 List of synthetic XUV spectra of GJ 3470
sp/* . 10 Individual synthetic XUV spectra of GJ 3470
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See also:
J/A+A/546/A27 : Radial velocity and photometry for GJ3470 (Bonfils+, 2012)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1 A1 --- Visit [A-F] Visit
3- 13 A11 --- Phase Phase (quiescent, flare, flare peak or
flare decay)
15- 56 A42 --- FileName Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 E10.5 0.1nm lambda Wavelength in stellar rest frame
17- 26 E10.5 10mW/m2/nm Flux Stellar flux (erg/cm2/Å/s)
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Acknowledgements:
Vincent Bourrier, vincent.bourrier(at)unige.ch,
Astronomical Observatory, University of Geneva, Switzerland
(End) V. Bourrier [Astronomical Obs., Geneva], P. Vannier [CDS] 17-Mar-2021