Classical chemically peculiar stars
• CP stars
• Upper main sequence stars
• Low rotational rate (< 100 km/s)
• Stable and organized stellar magnetic field
• Diffusion
• Spots
Classical chemically peculiar stars
Our stars
Our stars
Khokhlova et al., 2000, Astronomy Letters, 26, 177
Light variability due to He and Si
Krticka et al., 2007, A&A, 470, 1089
Light variability due to He and Si
Krticka et al., 2007, A&A, 470, 1089
Our stars
The HRD
Queiroz et al., 2018, MNRAS, 476, 2556
Bai et al., 2019, AJ, 158, 93 Gaia DR2
log g = log M + 4log(Teff) −
− log(L/L)
better log L
we need BC
Colour and Teff
Various calibrations can be
used to provide the colour
relation:
(B – V) = f(Teff)
Remember that observed
(B - V) must be corrected for
interstellar extinction to
(B - V)0
Most of the calibrations are for
cool type stars
Absorption = Extinction = Reddening
• AV = k1 E(B-V) = k2 E(V-R) = …
• General extinction because of the ISM characteristics
between the observer and the object
• Differential extinction within one star cluster because
of local environment
• Both types are, in general wavelength dependent
Absolute magnitude and bolometric
magnitude
• Absolute Magnitude M defined as apparent magnitude of a
star if it were placed at a distance of 10 pc
m – M = 5 log(d/10) - 5
where d is in pc
• Magnitudes are measured in some wavelength. To compare
with theory it is more useful to determine bolometric
magnitude Mbol – defined as absolute magnitude that would
be measured by a bolometer sensitive to all wavelengths. We
define the bolometric correction to be
BC = Mbol – MV
Bolometric luminosity is then
Mbol – Mbol, = -2.5 log L/L; Mbol, = 4.75 mag
Bolometric Correction
BC from Flower, 1996, ApJ, 469, 355
The HRD
2MASS, APASS and Gaia DR2 photometry, Gaia EDR3 astrometry
The HRD
The lifetime on the Main-Sequence
The lifetime on the Main-Sequence
Mass distribution