Campaign details
This STAROS campaign is dedicated to the observation of Sigma Geminorum (HD 62044), a K1 III star of magnitude 4.2.
We invite you to participate by using your spectrograph in “high spectral resolution” mode to follow the temporal evolution of the Hα line (for start), as well as the Ca II H and K lines (in a second time), in order to better understand its chromospheric activity.
How long ?
The Sigma Geminorum observation campaign will last 6 months.
Why Sigma Geminorum ?
Sigma Gem is a relatively bright star (V = 4.2) that lends itself well to high spectral resolution observations (resolution in excess of 13,000), and is accessible with telescopes and scopes of relatively modest diameters, from 80 mm aperture upwards. Sigma Gem also boasts some particularly interesting features:.
- Single-line spectroscopic binary: With a period of 19.6 days and a K amplitude of 34.8 km/s, Sigma Gem is an ideal target for cross-correlation techniques. This method, which is also used to detect exoplanets via radial velocity measurements, could pave the way for more ambitious scientific objectives.
- RS CVn chromospheric activity: Sigma Gem is an active RS CVn star, whose carefully observed Hα line reveals variations synchronized with its 19.6-day period. This activity is associated with the presence of spots similar to those observed on the Sun, which evolve over periods of a few stellar rotations. However, coordinated long-term observations are needed to better understand the origin and evolution of these active zones.
Visibility today at Paris
Campaign objectives ?
The main objective of this campaign is to observe the Hα line and its immediate surroundings. However, the chromospheric activity of this star is also visible in the center of the ultraviolet Ca II H and K lines, which constitutes a relevant secondary objective for this study. Complementary photometric observations would also be beneficial to better document these activity variations.
Observation guidelines
The main objective of this campaign is to observe the Hα line and its immediate surroundings. However, the chromospheric activity of this star is also visible in the center of the ultraviolet Ca II H and K lines, which constitutes a relevant secondary objective for this study. Complementary photometric observations would also be beneficial to better document these activity variations.
- Signal-to-noise ratio : A signal-to-noise ratio greater than 50 is desirable, and a value of 100 is an ideal target.
- Observation frequency: Observations should be made as frequently as possible, and spread over several observation cycles.
What to observe with?
The aim is to detect subtle variations in the profile of the Halpha line, which means that high spectral resolution is required to participate. The spectrograph must have a resolving power greater than or equal to R = 12000. Examples of such spectrographs include Shelyak's Lhires III, with a 2400 line/mm grating, and the Star'Ex HR spectrograph.
As for the instrument used, given the brightness, a telescope 60 mm or larger will provide very good data for this campaign. Large telescopes are also quite suitable, but it should be noted that here, small diameters (80 - 150 mm) are rather more advantageous, as the resolving power is then inherently high due to the narrowness of the entrance slit (aiming for R=18000 to R = 22000 may be an objective, but is not essential).
How to observe?
All recommendation for observations are precised on the dedicated page : How to observe .
If you have the opportunity, do one spectrum per clear night, or even two or three spectra per night, spaced a few hours apart.
Let’s go for this observing campaign, which will help us better understand the complex dynamics of Sigma Geminorum's chromospheric activity !