New STAROS campaign: sigma Gem (HD 62044)
Posted: Sat Apr 05, 2025 3:09 pm
Hello everyone,
We are delighted to launch a new collective spectroscopic observation campaign.
This time, the target is Sigma Geminorum, also known as HD 62044. It is a K1 III-type star with a visual magnitude of V = 4.2, well suited for high-resolution spectral observations, even with modest-diameter instruments (starting from a 70 mm aperture). This campaign is of particular interest, as K-type stars are still rarely targeted in high-resolution spectroscopy within our amateur observation programs. We are indeed more accustomed to observing hotter stars, such as Be stars.
The dedicated campaign website is here: https://sigmagem.staros-projects.org/
Scientific objectives:
Sigma Gem is a particularly interesting star from an astrophysical point of view. It is a single-lined spectroscopic binary with an orbital period of 19.6 days and a radial amplitude of 34.8 km/s. Moreover, Sigma Gem is an active RS CVn-type star, showing marked chromospheric activity clearly visible in the Hα line, with variations synchronized with its orbital period. This activity is associated with the presence of starspots, analogous to sunspots, which evolve over the star’s rotation. The main objective of this campaign is the detailed study of the Hα line and its temporal evolution.
Technical objective:
Another important goal of this campaign is to assess the accuracy of spectral calibration in lateral mode (injection of a neon reference light during acquisition). Indeed, since Sigma Gem is a relatively hot K-type star, telluric lines will be of little or no use for precise wavelength recalibration.
To ensure usable results and enable accurate comparative analyses, we recommend following these steps:
Minimum spectral coverage: 6530 Å to 6685 Å with a resolution >= 13000.
Signal-to-noise ratio: SNR >= 150 between 6650 and 6654 Å.
Using lateral mode for spectral calibration is recommended, with one or more fibers in front of your telescope or a neon lamp with a diffuser (tracing paper).
Before or after observing Sigma Gem, acquire a spectrum of a nearby hot star. We recommend Theta Gem (HD 50019), spectral type A2IV. This star is present in the Melchiors database. It must be calibrated in the same way as Sigma Gem.
Calculate the instrumental response using a Sigma Gem spectrum from the Melchiors database.
Process the spectrum of the hot star (e.g., HD 50019) to measure the average position of telluric lines. Then apply the measured average shift to the Sigma Gem spectrum. In any case, whether or not you used a reference star, check the calibration quality by performing an "atm check / telluric verification" under specINTI and look at the shift on the atmospheric line located at 6543.912 Å. Apply the shift if the value exceeds 0.05 Å.
Guillaume (for the STAROS team: Valérie, Matthieu, Olivier, and Christian)
To keep these campaigns going, host the data, and maintain the online analysis platforms, we need servers... and therefore support!
If you like what we’re doing, you can help keep the machine running (literally) by contributing to our infrastructure costs >>> https://staros-projects.org/en/support.html
We are delighted to launch a new collective spectroscopic observation campaign.
This time, the target is Sigma Geminorum, also known as HD 62044. It is a K1 III-type star with a visual magnitude of V = 4.2, well suited for high-resolution spectral observations, even with modest-diameter instruments (starting from a 70 mm aperture). This campaign is of particular interest, as K-type stars are still rarely targeted in high-resolution spectroscopy within our amateur observation programs. We are indeed more accustomed to observing hotter stars, such as Be stars.
The dedicated campaign website is here: https://sigmagem.staros-projects.org/
Scientific objectives:
Sigma Gem is a particularly interesting star from an astrophysical point of view. It is a single-lined spectroscopic binary with an orbital period of 19.6 days and a radial amplitude of 34.8 km/s. Moreover, Sigma Gem is an active RS CVn-type star, showing marked chromospheric activity clearly visible in the Hα line, with variations synchronized with its orbital period. This activity is associated with the presence of starspots, analogous to sunspots, which evolve over the star’s rotation. The main objective of this campaign is the detailed study of the Hα line and its temporal evolution.
Technical objective:
Another important goal of this campaign is to assess the accuracy of spectral calibration in lateral mode (injection of a neon reference light during acquisition). Indeed, since Sigma Gem is a relatively hot K-type star, telluric lines will be of little or no use for precise wavelength recalibration.
To ensure usable results and enable accurate comparative analyses, we recommend following these steps:
Minimum spectral coverage: 6530 Å to 6685 Å with a resolution >= 13000.
Signal-to-noise ratio: SNR >= 150 between 6650 and 6654 Å.
Using lateral mode for spectral calibration is recommended, with one or more fibers in front of your telescope or a neon lamp with a diffuser (tracing paper).
Before or after observing Sigma Gem, acquire a spectrum of a nearby hot star. We recommend Theta Gem (HD 50019), spectral type A2IV. This star is present in the Melchiors database. It must be calibrated in the same way as Sigma Gem.
Calculate the instrumental response using a Sigma Gem spectrum from the Melchiors database.
Process the spectrum of the hot star (e.g., HD 50019) to measure the average position of telluric lines. Then apply the measured average shift to the Sigma Gem spectrum. In any case, whether or not you used a reference star, check the calibration quality by performing an "atm check / telluric verification" under specINTI and look at the shift on the atmospheric line located at 6543.912 Å. Apply the shift if the value exceeds 0.05 Å.
Guillaume (for the STAROS team: Valérie, Matthieu, Olivier, and Christian)
To keep these campaigns going, host the data, and maintain the online analysis platforms, we need servers... and therefore support!
If you like what we’re doing, you can help keep the machine running (literally) by contributing to our infrastructure costs >>> https://staros-projects.org/en/support.html