EDP Sciences
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Volume 382, Number 1, January IV 2002
Page(s) 157 - 163
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011623

A&A 382, 157-163 (2002)
DOI: 10.1051/0004-6361:20011623

Asteroseismology from space: The $\delta$ Scuti star $\theta^2$ Tauri monitored by the WIRE satellite

E. Poretti1, D. Buzasi2, R. Laher3, J. Catanzarite4 and T. Conrow5

1  Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
2  Department of Physics, 2354 Fairchild Drive, US Air Force Academy, CO 80840, USA
3  SIRTF Science Center, California Institute of Technology, MS 314-6, Pasadena, CA 91125, USA
4  Interferometry Science Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
5  Infrared Processing and Analysis Center, California Insitute of Technology, MS 100-22, Pasadena, CA 91125, USA

(Received 16 October 2001 / Accepted 7 November 2001)

The bright variable star $\theta^2$ Tau was monitored with the star camera on the Wide-Field Infrared Explorer satellite. Twelve independent frequencies were detected down to the 0.5 mmag amplitude level. Their reality was investigated by searching for them using two different algorithms and by some internal checks: both procedures strengthened our confidence in the results. All the frequencies are in the range 10.8-14.6 cd -1. The histogram of the frequency spacings shows that 81% are below 1.8 cd -1; rotation may thus play a role in the mode excitation. The fundamental radial mode is not observed, although it is expected to occur in a region where the noise level is very low (55  $\mu$mag). The rms residual is about two times lower than that usually obtained from successful ground-based multisite campaigns. The comparison of the results of previous campaigns with the new ones establishes the amplitude variability of some modes.

Key words: methods: data analysis -- techniques: photometric -- stars: individual: $\theta^2$ Tau -- stars: oscillations -- stars: variable: $\delta$ Sct

Offprint request: E. Poretti, poretti@merate.mi.astro.it

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