3.1 Photometry

Since the discovery of the first indications of starspots, photometry remains the most common technique for studying stellar activity. Thanks to efforts of individual observers, more or less regular observations of spotted stars began in 1970’s. They are currently supported by a great number of Automatic Photometric Telescopes (APTs) which provide every-night routine measurements for a big sample of stars. At present, more than a dozen APTs with apertures of $20 cm$ to $1.2 m$ operate around the world (see Table 1). The accuracy of ground-based APTs is about $2 -5 mmag$ .


Observatory/APT	Location	Aperture	Filters


Catania	Mt. Etna, Sicily	$2 × 80 cm$	UBV
	http://www.ct.astro.it/sln/apt80.html
Fairborn	Patagonia, Arizona	$25- 80 cm$	UBV
	http://www.fairobs.org
Four-College $*$	Patagonia, Arizona	$80 cm$	UBVRI
Phoenix 10 $**$	Patagonia, Arizona	$25 cm$	UBV
http://www.fandm.edu/Departments/Astronomy/Phoenix10/Phoenix10.html
SAAO	Sutherland, South Africa	$75 cm$	UBVRI
	http://www.saao.ac.za/apt/
SpectraBot $+$	Morgan-Monroe, Indiana	$1.25 m$	UBVRI(CCD)
	http://www.astro.indiana.edu/spectrabot.html
STELLA II/AIP	Teide, Tenerife	$80 cm$	UBVRI(CCD), $uvby$ , $Ha$
Strömgren APT $++$	La Silla, Chile	$50 cm$	$uvby$ , $Hb$
	http://www.astro.ku.dk/~ijaf/0p5m.html
Wolfgang-Amadeus $#$	Patagonia, Arizona	$2 × 75 cm$	VRI, by
	http://www.aip.de/groups/activity/APT/

Table 1:

Automatic Photometric Telescopes collecting data for studying starspots. Remarks: $*$ Villanova, Cidadel, Charleston College, University of Nevada; $**$ Franklin & Marshal College; $+$ University of Indiana; $++$ Copenhagen Observatory; $#$ University of Vienna.

A vast amount of photometric data have been also obtained by the ESA mission HIPPARCOS with the accuracy down to $1 mmag$ (van Leeuwen et al., 1997 ). Future space missions aiming at studying stellar oscillations and detection of earth-size exoplanets will also provide immense high-precision photometry of nearby stars which can be used for studying starspots: