Airglow Lines
In the ultraviolet, the sky background contains important contributions from airglow lines, which vary from day to night and as a function of HST orbital position. Airglow lines may be an important consideration for spectroscopic observations at wavelengths near the lines. Both FUSE and HUT observed a variety of FUV airglow lines which may be present in COS data.
We have received requests for high-S/N observations of the geocoronal Lyman-alpha line profile observed with the G130M and G140L gratings. Such observations would allow users to model and subtract the line wings from their spectra. On this page, we provide a listing of both deliberate and serendipitous airglow observations. If you discover any others, please let us know through the HST Help Desk. To retrieve these datasets please use the HST archive.
Observations and Templates
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In these programs, COS airglow exposures were taken in parallel with STIS calibration observations.
Proposal Association Lifetime
PositionExposure Time Optical Element Central Wavelength (Å) 11860 LB8710060 1 2800s G140L 1105 11999 LBC402080 1 2500s G130M 1309 11999 LBC404040 1 1388s G130M 1309 12414 LBN6E2060 1 2900s G130M 1309 12414 LBN6E3060 1 2800s G130M 1291 12414 LBN6E4060 1 2800s G140L 1105 12775 LBW3E1060 1 2800s G130M 1291 12775 LBW3E2060 1 2800s G130M 1291 12775 LBW3E4060 2 2800s G140L 1105 13145 LC4KE1060 2 2900s G130M 1291 13145 LC4KE2060 2 2560s G130M 1291 13145 LC4KE3060 2 2900s G130M 1291 13145 LC4KE4060 2 2900s G130M 1291 13548 LCETE1060 2 2900s G130M 1327 13548 LCETE2060 2 2272s G130M 1327 13548 LCETE3060 2 2900s G130M 1327 13548 LCETE4060 2 2900s G130M 1327 13548 LCETE5060 2 2900s G130M 1327 13994 LCQJE3060 3 2900s G130M 1291 13994 LCQJE4060 3 2900s G130M 1291 14429 LD1CE1060 3 2900s G130M 1327 14429 LD1CE2060 3 2900s G130M 1327 14429 LD1CE3060 3 2900s G130M 1291 14429 LD1CE4060 3 2900s G130M 1291 14833 LDBUE2060 3 2900s G130M 1327 -
Observations will be posted as they are released to the public.
Proposal Association Lifetime
PositionExposure Time Optical Element Central Wavelength (Å)
11522 LB6203010 1 1150s G130M 1291 11522 LB6203020 1 1150s G130M 1318 11616 LB6B29010 1 954s G130M 1291 11616 LB6B29020 1 954s G130M 1327 11616 LB6B29030 1 642s G160M 1577 11616 LB6B29040 1 642s G160M 1600 11616 LB6B29050 1 642s G160M 1623 11727 LB5B01010 1 2070s G130M 1309 11727 LB5B01020 1 2830s G160M 1623 12034 LBGH04010 1 810s G130M 1309 12034 LBGH04020 1 810s G130M 1327 12034 LBGH04030 1 454s G160M 1589 12034 LBGH04040 1 1280s G160M 1600 12034 LBGH04050 1 1495s G160M 1577 12169 LBIYAM010 1 1460s G130M 1291 12426 LBNM01010 1 2800s G160M 1577 12426 LBNM01020 1 2850s G160M 1589 12426 LBNM01030 1 2750s G160M 1600 12426 LBNM01040 1 2800s G160M 1611 12426 LBNM01050 1 3350s G160M 1623 12275 LBH408010 1 1381s G130M 1327 12275 LBH408020 1 5926s G130M 1291 12275 LBH458010 1 1381s G130M 1327 12275 LBH458020 1 5926s G130M 1291 12870 LC1VA8010 2 6944s G140L 1105 13302 LC8008010 2 5460s G140L 1105 13456 LC9502010 2 16549s G160M 1577 -
Dr. Vincent Bourrier of Geneva Observatory and his team, used a recent set of COS observations of 55 Cnc to build observational templates of four airglow lines and used them successfully to decontaminate the observations, as outlined in High-energy environment of super-Earth 55 Cnc e. Bourrier et al. have graciously offered to share these templates with the greater astronomy community through STScI. They caution that the lines in the templates are not centered on their rest wavelengths and have an arbitrary flux scaling. Users wishing to make use of these templates should fit the position and amplitude of the templates according to their observations, as these properties are specific to a given observation that was obtained with the COS G130M grating at a central wavelength of 1291 Å with the Hubble Space Telescope.
The templates can be seen in the paper in the following figures:
- OI line (rest wavelength 1304.8576 Å) in Fig. 4
- OI line (rest wavelength 1306.0286 Å) in Fig. 4
- OI line (rest wavelength 1302.1685 Å) in Fig. 5
- HI line (rest wavelength 1215.6702 Å) in Fig. 6
The four tables follow the same structure. They contain three columns:
- The wavelength, in angstroms
- The flux of a given geocoronal emission line, in erg/cm²/Å/s
- The associated errors, in erg/cm²/Å/s
STScI and the COS Team have not tested these templates and while we encourage the astronomy community to make use of these products, we warn users to do so at their own risk.
Line (Å) Optical Element Central Wavelength (Å) Template OI 1302 G130M 1291 airglow_OI_1302.dat OI 1305 G130M 1291 airglow_OI_1305.dat OI 1306 G130M 1291 airglow_OI_1306.dat HI 1216 G130M 1291 airglow_HI_1216.dat -
Below is a table of FUV airglow lines which may be present in your COS observations. These lines are were compiled by Paul Feldman from FUSE and HUT observations*.
Additional Information:
- Lines grouped together may be blended;
- A range of wavelengths indicates multiple features at nearly the same wavelength;
- Only the Lyman series features will be strong during the night. However, if your observation is taken close to the bright earth limb, the strongest daytime airglow lines of other species may also be present.
- While COS has a similar resolution to FUSE, HUT had a resolution of about 2.5 Å;
- FUSE and HUT had much larger apertures than COS;
*Feldman et al. (2001, JGR, 106, 8119) present an extensive set of airglow spectra observed with FUSE
Wavelength (Å) Species Strength (Day) Source Notes 832.76-834.46 O II S HUT 860.2 O II VW HUT Second order from 430.1 878.9-879.6 O I VW HUT 907 N I W HUT Multiple lines 915-916.7 N II W HUT 920.963 H I VW FUSE 923.150 H I W FUSE 926.226
926.295H I
O IW
WFUSE
FUSE929.517 O I VW FUSE 930.748 H I W FUSE 936.630 O I W FUSE 937.803 H I W FUSE 948.686 O I W FUSE 949.743
950.112H I
O IM
FUSE
FUSE950.733 O I W FUSE 953.4 - 954.0 N I W HUT 958 N2 c4' VW HUT 964.0 - 965.0 N I W HUT 971.738 O I W FUSE 972.537 H I W FUSE 973.234 O I W FUSE 973.885 O I W FUSE 976.4-978.6 O I W HUT 988.773
988.655O I
O IS
MFUSE
FUSECheck strength; these are strong when blended 990.204
990.123O I
O IW
FUSE
FUSE990.801 O I W FUSE 1009.4 - 1010.6 O II? VW HUT 1025.722
1025.762H I
O IS
MFUSE
FUSECheck strength; these are strong when blended 1027.431 O I W FUSE 1039.230 O I M FUSE 1040.943 O I W FUSE 1041.688 O I W FUSE 1044.426 He I W FUSE Second order from 522.213 1074.060 He I M FUSE Second order from 537.030 1078 O II M HUT Second order from 539.5 1084.580 N II W FUSE 1085.701 N II W FUSE 1110.2 O II VW HUT Second order 555.1 1134.165
1134.415N I
N IM
MFUSE
FUSECheck strength; these are strong when blended 1134.980 N I M FUSE 1152.15 O I W HUT 1162 O II W HUT Second order from 580.7 1168.668 He I S FUSE Second order from 584.334 1199.5 - 1200.7 N I S HUT 1215.67 H I VS HUT 1228.6 N I HUT Masked by scattered Lyman-α in HUT spectra 1233.2 O II HUT Masked by scattered Lyman-α in HUT spectra; second order from 616.6 1243.3 N I HUT Masked by scattered Lyman-α in HUT spectra 1302.2 - 1306.0 O I VS HUT 1355.6
1358.5O I
O IS
SHUT 1437 O II VW HUT Second order from 718.5 1492.6 - 1494.7 N I W HUT 1566 He I VW HUT Third order from 522.21 1611 He I VW HUT Third order from 537.02 1618 O II VW HUT Third order from 539.5 1641.3 O I W HUT 1752 He I M HUT Third order from 584.33 -
The subtractAirglow tool is an open-source Python code that can be used to fit airglow profiles of HI and OI lines to COS observations, subtract them, and reconstruct the underlying emission line of the source. The code is optimized for F, G, K, and M dwarf stars, but it can be used for other targets observed with COS G130M.
The code is described in this paper: Cruz Aguirre et al. 2023: Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra]. It is publicly available in the following GitHub repository: https://github.com/AstroAguirre/subtractAirglow. This tool has a user-friendly Graphics User Interface (GUI), and the repository contains basic instructions on operating the GUI.
The COS Team has tested this code and verified its usability and accuracy in a limited test data set. While we encourage the astronomy community to use this product, we warn users to do so at their own risk.
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