Epidemiología de la infección

HIP 114379 E HIP 114385 HIP 114379 Nov '01 _{Jun '02} N

Figure 4.35: The adaptive optics H-band image of HIP 114379 and HIP 114385 taken with the AO system ALFA and the camera Ω Cass at Calar Alto, Spain. Note the circled star which could be a low-mass companion, but which is not yet confirmed. The estimated mass of the low-mass object assuming it is bound to the system is 0.05 M¯.

the high resolution ALFA adaptive optics image closely, one can see a faint object north-east of HIP 114379 which is marked with a circle. Assuming it is at the same distance, using the H- band photometry we estimate the mass to 0.05 M_¯ (brown dwarf) at a separation of 207 AU. The object must be confirmed to be a low mass companion by proper motion measurements and spectroscopy. The proper motion measurement within this half year does not yet lead to a clear conclusion. Within the error the faint companion candidate could or could not be comoving.

The two bright objects have almost the same brightness and one object is a single star, we could perform a point spread function subtraction, which means, we scale the maximum count in the single star to the maximum count level of the binary star and then subtract the single star from the binary. It worked and only light from SB2 secondary is left over so that it was made visible.

4.10

β

Pictoris moving group

The star β Pictoris was identified to be an isolated young star by Jura et al. (1993). Later Barrado y Navascu´es et al. (1999) found that the stars GJ 799 and GJ 803 are comoving with β Pic. They estimated an age of 20±10 Myr for the three stars.

Starformation scenarios agree that relative massive stars such as β Pic form in clusters or associations with dozens of members. These associations dissociate in time but at the estimated age of∼20 Myr one expects still to find comoving members. And indeed Zuckerman et al. (2001a) identified 15 additional members. The average distance from the sun of these 18 stars is ∼ 35 pc and its mean space motion is U = −10.5 km/s, V = −15.8 km/s, V =

−9.5 km/s. The stars are located in the range of Ra: 00h to 21h and Dec: -02◦ _{20m to -72}◦

82 4 FLARE STARS IN STELLAR ASSOCIATIONS

4.10.1 [GKL 99] 82, HIP 13402, HD 17925

The iron abundance of this star is [Fe/H]= +0.083±0.038 taken from Taylor (2003). Habing et al. (2001) give aV = 6.05 mag and a temperature ofT_eff = 5000 K measured with Geneva photometry. They suggest an age of 80 Myr and it has a distance of d = 10.4 pc. Around the star is a disk. Wichmann et al. (2003) measuredWm

Li = 215 ˚A which they corrected for the nearby iron absorption to Wc

Li = 194 ˚A. The radial velocity is vrad = 18.2 km/s with a vsini <10 km/s. The space motion isU =−5.4 km/s, V =−16.6 km/s, andW =−2.1 km/s which makes it consistent with theβ Pictoris moving group or local association. Montes et al. (2001) list it as a member of the local association. Cayrel de Strobel & Cayrel (1989) suggest that the birth place of the star lies in the Scorpio-Centaurus-Complex.

4.10.2 [GKL 99] 145, HIP 26779

The space motion of this star (U =−14.0±0.7 km/s, V =−23.0±0.4 km/s, W =−14.2±

0.2 km/s) is consistent with the β Pictoris moving group or the local association.

Analyzing the FOCES spectra, we get very good agreement of the spectroscopic distance with the Hipparcos distance with a discrepancy of only 0.5%.

Teff logg [Fe/H] vsini mV Mbol mass

[K] [km/s] [mag] [mag] M¯

5260±70 4.50±0.10 0.09±0.07 3.10±1.00 6.12 5.43 0.90

Table 4.13: Spectral parameters of HIP 26779.

Comparing with the photometric metallicity abundance, Haywood (2001) measures a value of -0.01 dex, while Gaidos & Gonzalez (2002) measure 0.08±0.04 dex and an effective temper- ature of 5295±47 K in good agreement with our data.

4.10.3 [GKL 99] 132, HIP 23200

The space motion is (U/V /W) = (−11.3±0.7/−16.9±0.9/−9.1±0.4) km/s. Its location in the northern hemisphere (Ra: 04 h 59 m 04.8 s, Dec: 01◦ ₄₇m ₀₁2_{) could make it the most} northern member of β PicA but it has a fairly high lithium abundance of logN(Li) = 1.5 at a spectral type M0V and its Hα emission with an equivalent width of 1.9 ˚A shows that the star is fairly young, younger than the Pleiades given the lithium abundance. Christian & Mathioudakis (2002) also observed this star and they measure a lithium abundance of logN(Li) = 1.5 and an Hα-emission line with an equivalent width of 1.4 ˚A. Its position in the Siess et al. (2000) models makes it consistent with theβ PicA member stars with 20±10 Myr. We propose this star to be a member candidate of theβ Pic association.

4.10.4 [GKL 99] 137 and [GKL 99] 136, or GJ 3331 A & B

The visual binary GJ 3331 A & B consists of two stars with M2V and M3V. It is located in the line of sight of theβ PicA. For these stars no distance measurement is available. We have observed them from La Silla, ESO using the DFOSC instrument. The A component shows Hα in emission (EW(Hα) = 1.8 ˚A) and a lithium abundance comparable with the Pleiades (EW(Li) = 0.06 ˚A). The lithium abundance is too low for the star to be a member ofβ PicA. GJ 3331 B does not show any signatures of youth or chromospheric activity in its DFOSC- spectrum.