How would one estimate the rotation period of a star from its spectrum

In summary, the conversation discusses a figure showing measurements taken on two consecutive observing nights. The ordinate represents the flux normalized to continuum and the abscissa represents the wavelength scale. The "bumps" on the profile, indicated by arrows, refer to a starspot that moves across the surface of the star as it rotates. The conversation mentions difficulty in estimating the rotational period based on the wavelength scale. A relevant study on starspots is also referenced.
  • #1
SJay16
19
1
Homework Statement
Using the profiles in Figure 18.29, make an estimate for the rotation period of σ Gem.
Relevant Equations
N/A
Screenshot (156).png

The figure is shown; the measurements were taken on two consecutive observing nights. The Ordinate is the flux normalized to continuum and the abscissa is the wavelength scale. You can see the "bumps" indicated by the arrows referring to some Starspot as the spot moves on the profile; assuming a single time-stable position-stable spot.

The "bumps" slightly shifts, as indicated by the arrows in the top line profile compared to the bottom profile, as the spot "moves across" the surface as the star as it rotates; I'm just not sure how to get an estimate of the rotational period from this given just the wavelength for the abscissa, it would make sense if the abscissa was on a timescale.

Figure reference : Gray, D. (2005). The Observation and Analysis of Stellar Photospheres (3rd ed.), page 498. Cambridge: Cambridge University Press. doi:10.1017/CBO9781316036570
 
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FAQ: How would one estimate the rotation period of a star from its spectrum

How is the rotation period of a star estimated from its spectrum?

The rotation period of a star can be estimated by measuring the Doppler shift of spectral lines caused by the rotation of the star. As the star rotates, one side moves towards us and the other side moves away from us, causing the spectral lines to shift in wavelength. By measuring the amount of this shift, the rotation period can be calculated.

What is the relationship between the rotation period and spectral line broadening?

There is a direct relationship between the rotation period of a star and the broadening of its spectral lines. As the star rotates faster, the spectral lines become broader due to the Doppler shift. This means that the broader the spectral lines, the shorter the rotation period of the star.

Can the rotation period of a star be estimated from its spectrum alone?

Yes, the rotation period of a star can be estimated from its spectrum alone. However, it is important to note that other factors such as the inclination of the star's rotation axis and the presence of spots or magnetic fields can also affect the spectral lines and need to be taken into consideration.

How accurate is the estimation of rotation period from a star's spectrum?

The accuracy of the rotation period estimation from a star's spectrum depends on various factors such as the quality of the spectral data, the rotational velocity of the star, and the presence of any other factors that may affect the spectral lines. In general, the estimation can be accurate to within a few percent.

Can the rotation period of all types of stars be estimated from their spectra?

Yes, the rotation period of all types of stars can be estimated from their spectra. However, the method used for estimation may vary depending on the type of star. For example, for rapidly rotating stars, a more sophisticated method such as Fourier transform analysis may be needed to accurately measure the rotation period.

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