In-flight radiometric calibration of the Metis UV H I Ly-α channel and comparison with UVCS data

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985815%3A_____%2F25%3A00636189" target="_blank" >RIV/67985815:_____/25:00636189 - isvavai.cz</a>

Result on the web

<a href="https://hdl.handle.net/11104/0367209" target="_blank" >https://hdl.handle.net/11104/0367209</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1051/0004-6361/202450759" target="_blank" >10.1051/0004-6361/202450759</a>

Result language

angličtina

Original language name

In-flight radiometric calibration of the Metis UV H I Ly-α channel and comparison with UVCS data

Original language description

We present the results of the in-flight radiometric calibration performed for the ultraviolet (UV) H I Ly-alpha channel of the Metis coronagraph on board Solar Orbiter. Aims. The radiometric calibration is a fundamental procedure required to produce data in physical units. The quantity that allows us to pass from raw data into calibrated data is the radiometric calibration factor ϵUV. Methods. To obtain the ϵUV results, we used observations of stellar targets transiting the Metis field of view. We derived ϵUV by determining the signal of each calibration star by means of the aperture photometry and evaluating its expected flux in the Metis narrow bandpass (121.6 +/- 10 nm). The analyzed data cover a time range from the beginning of the Cruise Phase in June 2020, up until August 2021. Results. We find that the UV channel requires a significant additional correction of the response across the field of view, compared to that provided by the vignetting function measured on the ground and refined in flight, specifically tailored to the UV channel. This correction is provided by the ratio of images of the back-illumination of the closed door. Here, we use the stellar measurements to refine and improve such a correction map. After correcting for the spatial disuniformity, a radiometric calibration factor ϵUV = 0.20 +/- 0.03 DN/photon was found. No significant changes in the UV channel throughput were observed during the period from June 2020 to August 2021. In addition, the analysis of a smaller number of stars observed in 2022 and 2023 enabled us to extend the validity of the radiometric calibration to that period, after considering a suitable scaling factor due to the change of operating voltages occurred in April 2022. From this second analysis, the value of the radiometric calibration factor is ϵUV = 0.11 +/- 0.03 DN/photon. In order to support the radiometric calibration results, we performed a comparison between average radial profiles of the H I Ly-alpha intensity obtained from Metis UV images acquired in 2020-2021 and those measured with the Ultra-Violet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO) during the period of the activity minimum of solar cycle 22 in 1996. We found that intensity profiles of these instruments are consistent with each other.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

—

OECD FORD branch

10308 - Astronomy (including astrophysics,space science)

Project

<a href="/en/project/GA22-34841S" target="_blank" >GA22-34841S: Science with Solar Orbiter: Focusing on eruptive processes</a><br>

Continuities

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Publication year

2025

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Name of the periodical

Astronomy & Astrophysics

ISSN

0004-6361

e-ISSN

1432-0746

Volume of the periodical

697

Issue of the periodical within the volume

May

Country of publishing house

FR - FRANCE

Number of pages

13

Pages from-to

A73

UT code for WoS article

001486834100005

EID of the result in the Scopus database

2-s2.0-105005299801