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

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SUMMARY

The discussion focuses on estimating the rotation period of a star using spectral data, specifically analyzing the flux and wavelength measurements taken over two consecutive nights. The presence of "bumps" in the spectral profile indicates starspots moving across the star's surface, which can be correlated to its rotation. The challenge lies in converting the wavelength data into a time scale to derive the rotational period. Reference is made to Gray, D. (2005) for further insights into stellar photosphere analysis.

PREREQUISITES
  • Understanding of stellar spectroscopy and flux measurements
  • Familiarity with starspot dynamics and their impact on spectral profiles
  • Knowledge of rotational dynamics in astrophysics
  • Access to Gray, D. (2005). The Observation and Analysis of Stellar Photospheres
NEXT STEPS
  • Research techniques for converting wavelength data into time scales for stellar rotation
  • Explore Doppler imaging methods for analyzing starspots
  • Study the impact of starspot movement on spectral line profiles
  • Investigate software tools for spectral analysis in astrophysics
USEFUL FOR

Astronomers, astrophysicists, and students studying stellar dynamics and spectroscopy will benefit from this discussion, particularly those interested in estimating stellar rotation periods.

SJay16
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Homework Statement
Using the profiles in Figure 18.29, make an estimate for the rotation period of σ Gem.
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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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