Predicting Lyα and Mg II fluxes from K and M dwarfs using galaxy evolution explorer ultraviolet photometry

Evgenya Shkolnik, Kristina A. Rolph, Sarah Peacock, Travis S. Barman

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

A star's ultraviolet (UV) emission can greatly affect the atmospheric chemistry and physical properties of closely orbiting planets with the potential for severe mass loss. In particular, the Lyα emission line at 1216 A˚, which dominates the far-ultraviolet (FUV) spectrum, is a major source of photodissociation of important atmospheric molecules such as water and methane. The intrinsic flux of Lyα, however, cannot be directly measured due to the absorption of neutral hydrogen in the interstellar medium and contamination by geocoronal emission. To date, reconstruction of the intrinsic Lyα line based on Hubble Space Telescope spectra has been accomplished for 46 FGKM nearby stars, 28 of which have also been observed by the Galaxy Evolution Explorer (GALEX). Our investigation provides a correlation between published intrinsic Lyα and GALEX far- and near-ultraviolet (NUV) chromospheric fluxes for K and M stars. The negative correlations between the ratio of the Lyα to the GALEX fluxes reveal how the relative strength of Lyα compared to the broadband fluxes weakens as the FUV and NUV excess flux increase. We also correlate GALEX fluxes with the strong NUV Mg II h+k spectral emission lines formed at lower chromospheric temperatures than Lyα. The reported correlations provide estimates of intrinsic Lyα and Mg II fluxes for the thousands of K and M stars in the archived GALEX all-sky surveys. These will constrain new stellar upper atmosphere models for cool stars and provide realistic inputs to models describing exoplanetary photochemistry and atmospheric evolution in the absence of UV spectroscopy.

Original languageEnglish (US)
Article numberL20
JournalAstrophysical Journal Letters
Volume796
Issue number1
DOIs
StatePublished - Nov 20 2014
Externally publishedYes

Fingerprint

ultraviolet photometry
dwarf galaxies
galaxies
K stars
M stars
geocoronal emissions
A stars
atmospheric chemistry
photochemistry
cool stars
upper atmosphere
spectral emission
ultraviolet emission
ultraviolet spectroscopy
ultraviolet spectra
Hubble Space Telescope
photochemical reactions
photodissociation
planet
physical property

Keywords

  • planet-star interactions
  • stars: activity
  • stars: atmospheres
  • stars: chromospheres

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Predicting Lyα and Mg II fluxes from K and M dwarfs using galaxy evolution explorer ultraviolet photometry. / Shkolnik, Evgenya; Rolph, Kristina A.; Peacock, Sarah; Barman, Travis S.

In: Astrophysical Journal Letters, Vol. 796, No. 1, L20, 20.11.2014.

Research output: Contribution to journalArticle

@article{329b32b01c3e469dac6aefa9726b9291,
title = "Predicting Lyα and Mg II fluxes from K and M dwarfs using galaxy evolution explorer ultraviolet photometry",
abstract = "A star's ultraviolet (UV) emission can greatly affect the atmospheric chemistry and physical properties of closely orbiting planets with the potential for severe mass loss. In particular, the Lyα emission line at 1216 A˚, which dominates the far-ultraviolet (FUV) spectrum, is a major source of photodissociation of important atmospheric molecules such as water and methane. The intrinsic flux of Lyα, however, cannot be directly measured due to the absorption of neutral hydrogen in the interstellar medium and contamination by geocoronal emission. To date, reconstruction of the intrinsic Lyα line based on Hubble Space Telescope spectra has been accomplished for 46 FGKM nearby stars, 28 of which have also been observed by the Galaxy Evolution Explorer (GALEX). Our investigation provides a correlation between published intrinsic Lyα and GALEX far- and near-ultraviolet (NUV) chromospheric fluxes for K and M stars. The negative correlations between the ratio of the Lyα to the GALEX fluxes reveal how the relative strength of Lyα compared to the broadband fluxes weakens as the FUV and NUV excess flux increase. We also correlate GALEX fluxes with the strong NUV Mg II h+k spectral emission lines formed at lower chromospheric temperatures than Lyα. The reported correlations provide estimates of intrinsic Lyα and Mg II fluxes for the thousands of K and M stars in the archived GALEX all-sky surveys. These will constrain new stellar upper atmosphere models for cool stars and provide realistic inputs to models describing exoplanetary photochemistry and atmospheric evolution in the absence of UV spectroscopy.",
keywords = "planet-star interactions, stars: activity, stars: atmospheres, stars: chromospheres",
author = "Evgenya Shkolnik and Rolph, {Kristina A.} and Sarah Peacock and Barman, {Travis S.}",
year = "2014",
month = "11",
day = "20",
doi = "10.1088/2041-8205/796/1/L20",
language = "English (US)",
volume = "796",
journal = "Astrophysical Journal Letters",
issn = "2041-8205",
publisher = "IOP Publishing Ltd.",
number = "1",

}

TY - JOUR

T1 - Predicting Lyα and Mg II fluxes from K and M dwarfs using galaxy evolution explorer ultraviolet photometry

AU - Shkolnik, Evgenya

AU - Rolph, Kristina A.

AU - Peacock, Sarah

AU - Barman, Travis S.

PY - 2014/11/20

Y1 - 2014/11/20

N2 - A star's ultraviolet (UV) emission can greatly affect the atmospheric chemistry and physical properties of closely orbiting planets with the potential for severe mass loss. In particular, the Lyα emission line at 1216 A˚, which dominates the far-ultraviolet (FUV) spectrum, is a major source of photodissociation of important atmospheric molecules such as water and methane. The intrinsic flux of Lyα, however, cannot be directly measured due to the absorption of neutral hydrogen in the interstellar medium and contamination by geocoronal emission. To date, reconstruction of the intrinsic Lyα line based on Hubble Space Telescope spectra has been accomplished for 46 FGKM nearby stars, 28 of which have also been observed by the Galaxy Evolution Explorer (GALEX). Our investigation provides a correlation between published intrinsic Lyα and GALEX far- and near-ultraviolet (NUV) chromospheric fluxes for K and M stars. The negative correlations between the ratio of the Lyα to the GALEX fluxes reveal how the relative strength of Lyα compared to the broadband fluxes weakens as the FUV and NUV excess flux increase. We also correlate GALEX fluxes with the strong NUV Mg II h+k spectral emission lines formed at lower chromospheric temperatures than Lyα. The reported correlations provide estimates of intrinsic Lyα and Mg II fluxes for the thousands of K and M stars in the archived GALEX all-sky surveys. These will constrain new stellar upper atmosphere models for cool stars and provide realistic inputs to models describing exoplanetary photochemistry and atmospheric evolution in the absence of UV spectroscopy.

AB - A star's ultraviolet (UV) emission can greatly affect the atmospheric chemistry and physical properties of closely orbiting planets with the potential for severe mass loss. In particular, the Lyα emission line at 1216 A˚, which dominates the far-ultraviolet (FUV) spectrum, is a major source of photodissociation of important atmospheric molecules such as water and methane. The intrinsic flux of Lyα, however, cannot be directly measured due to the absorption of neutral hydrogen in the interstellar medium and contamination by geocoronal emission. To date, reconstruction of the intrinsic Lyα line based on Hubble Space Telescope spectra has been accomplished for 46 FGKM nearby stars, 28 of which have also been observed by the Galaxy Evolution Explorer (GALEX). Our investigation provides a correlation between published intrinsic Lyα and GALEX far- and near-ultraviolet (NUV) chromospheric fluxes for K and M stars. The negative correlations between the ratio of the Lyα to the GALEX fluxes reveal how the relative strength of Lyα compared to the broadband fluxes weakens as the FUV and NUV excess flux increase. We also correlate GALEX fluxes with the strong NUV Mg II h+k spectral emission lines formed at lower chromospheric temperatures than Lyα. The reported correlations provide estimates of intrinsic Lyα and Mg II fluxes for the thousands of K and M stars in the archived GALEX all-sky surveys. These will constrain new stellar upper atmosphere models for cool stars and provide realistic inputs to models describing exoplanetary photochemistry and atmospheric evolution in the absence of UV spectroscopy.

KW - planet-star interactions

KW - stars: activity

KW - stars: atmospheres

KW - stars: chromospheres

UR - http://www.scopus.com/inward/record.url?scp=84909979675&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84909979675&partnerID=8YFLogxK

U2 - 10.1088/2041-8205/796/1/L20

DO - 10.1088/2041-8205/796/1/L20

M3 - Article

VL - 796

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

SN - 2041-8205

IS - 1

M1 - L20

ER -