Therefore, I collected the S-indices from different catalogues (e. g., Duncan et al. (1991);
Wright et al. (2004)). Thereafter, the S-indices are sorted by luminosity class and by colour indexB−V and selected those objects with the smallest S-index for each luminosity class (giant, subgiant and main sequence star) and for B−V. Next, I checked if the object has been detected in X-rays because active stars are bright in X-ray. Finally, the rotation periodP and the rotation velocity (vsini), respectively, are checked as only slow rotators are usable as templates.
Additionally, I observed flat active stars (see. Sect. 6.4.2) with a small S-index and non detected stars (see. Sect. 6.4.2) from the sample by Baliunas et al. (1995) and Hall et al.
(2007), respectively, in order to check if these stars are usable as template stars. These stars are selected from the object list which was used to create the transformation equation form the S-index of the HRT to the Mount Wilson S-index.
8.2 Observed template star candidates 105
Object S log R′HK
HD32923 0.140±0.005 −5.15±0.09.
HD58855 0.147±0.005 −5.12±0.10.
HD84737 0.137±0.005 −5.19±0.10.
HD89744 0.144±0.006 −5.15±0.11.
HD124570 0.130±0.006 −5.44±0.21.
HD142373 0.146±0.006 −5.11±0.12.
Table 8.2: The objects with S-index S and the log RHK′
velocity and a metallicity for each object. In order to decide if a star can be used as a template one has to take into account the rotational velocity. To compare different stars, their metallicities can influence the value of the flux excess.
HD32923is also called 104 Tau. This star is one of the stars from the star sample which was used to create the transformation equation fromSHRT toSMWO. It was selected from Hall et al. (2007). For this object, a long-term variability was not detected and the average S-index ishSi= 0.143 (Hall et al. 2007). The S-index was also measured for this object by Wright et al. (2004) and by Gray et al. (2003) as S = 0.155 and S = 0.142, respectively.
The here measured S-index (0.140±0.006) is comparable with the values by Hall et al.
(2007) and by Gray et al. (2003). The S-index by Wright et al. (2004) is significantly different from all other measurements.
HD32923 has a rotational velocity and metallicity ofvsini = (1.6±0.6) km/s (Glebocki and Stawikowski 2000) and [F e/H] =−0.22 (Holmberg et al. 2009), respectively.
In Fig. 8.1, the Caii H+K lines of HD32923 are shown. This spectrum was taken on
Figure 8.1: The Caii H+K lines of HD32923 observed at Jan. 5 2009, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 2); left:
Caii K line with a S/N of 33 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 40 electrons/pixel in 1 ˚A bandpass
Figure 8.2: The Ca II H+K lines of HD58855 observed at Feb. 12 2009, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 2); left:
Caii K line with a S/N of 68 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 81 electrons/pixel in 1 ˚A bandpass
Jan. 5 2009 with an exposure time of 3600 sec. In the rebinned spectrum, one can see a weak double peak structure in the CaiiK line whereas in the CaiiH line there is no such feature. I conclude that this spectrum shows a weak sign of activity.
HD58855 is also called 22 Lyn and was selected from Duncan et al. (1991). The total number of observation is 3 and the average S-index ishSi= (0.150±0.001) (Duncan et al.
1991). To compare this value with the S-index of this measurement (0.147±0.005), both S-indices agree within the errors.
The rotational velocity and metallicity of this object arevsini= 8.5 km/s (Schr¨oder et al.
2009) and [F e/H] =−0.28 (Holmberg et al. 2009), respectively.
The spectral ranges of the CaiiH+K lines of HD58855 are shown in Fig. 8.2. This figure shows the co-added spectrum of 3 single observations on Feb. 12 2009. The total exposure time was 10800 sec. In the Caii H+K lines (Fig. 8.2), no double peak structure can be seen.
It is also possible to calculate a rotation period and I obtained a value ofP = (16.4±11.5) day with Eq. 7.16. The large error is the result of the errors of the equation parameters.
Without these parameter errors, I obtain an error ofσ= 1.6 days.
This object does not show any activity signs in its spectrum (Fig. 8.2). Therefore, this object is a very good template candidate.
HD84737 is also called 15 LMi and was selected from Duncan et al. (1991). The total number of observations is one with a S-index ofS = 0.145. The S-index was also deter-mined by Wright et al. (2004) asS = 0.130 and by Gray et al. (2003) asS= 0.140. These three S-indices are clearly different. The S-index of this measurement is (0.137±0.005).
The object has a rotational velocity ofvsini= (2.8±0.8) km/s (Glebocki and Stawikowski 2000) and a metallicity of [F e/H] = 0.07 (Holmberg et al. 2009).
The Caii H+K lines of HD84737 are shown in Fig. 8.3. This spectrum is a co-added
8.2 Observed template star candidates 107
Figure 8.3: The Ca II H+K lines of HD84737 observed at Feb. 11 2009, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 2); left:
Caii K line with a S/N of 49 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 57 electrons/pixel in 1 ˚A bandpass
spectrum of 2 single observations on Feb. 11 2009 with a total exposure time of 7200 sec.
In the spectrum of the Caii K line (Fig. 8.3), one sees on the left side of the line core a weak peak. Here, it is not definitely clear whether this peak is caused by activity or by dark noise. Though, because of the missing of a weak peak on the right side of the line core, one can assume that this peak is created by the dark noise. The latter assumption is possible because in the Caii H line (Fig. 8.3), one does not see a double peak structure.
This object is a good template candidate with a small log R′HK even though the Caii K line shows a peak.
HD89744 is labelled as flat active star in Baliunas et al. (1995) and is one of the stars which was used for S-index calibration (Sect. 6.4.2). The average S-index ishSi= 0.137.
The S-index in Wright et al. (2004) isS = 0.158 and in Gray et al. (2003)S= 0.137. The S-index for this measurement is (S = 0.144±0.006). The rotational velocity and metallic-ity of HD89737 arevsini= 10 km/s (Glebocki and Stawikowski 2000) and [F e/H] = 0.18 sun (Holmberg et al. 2009), respectively. For this object, X-ray radiation was detected with a count rate of (1.139±0.151)·10−2 ct/s (Second ROSAT PSPC Catalog 2000).
In Fig. 8.4, the Caii H+K lines of HD89744 are shown. It is a co-added spectrum of 3 single observations on Dec. 29 2008. The total exposure time was 8100 sec.
The Caii K line (Fig. 8.4) is too noisy to detect a peak structure. In the rebinned spec-trum of the CaiiK line, it is also not possible to detect the double peak structure. On the other hand, one can see a very weak double peak structure in the Caii H line. Therefore, I can conclude, it is possible that this object has a very low activity level.
HD124570is also called 14 Boo and is one of the stars from the star sample which was used to perform the S-index calibration (Sect. 6.4.2). The average S-index ishSi= 0.133 and the star is labelled as flat active star by Baliunas et al. (1995) and by Hall et al.
(2007) as ”not detected” with an average S-index of hSi = 0.134. The S-index for this
Figure 8.4: The Ca II H+K lines of HD89744 observed at Dec. 29 2008, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 29; left:
Caii K line with a S/N of 34 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 36 electrons/pixel in 1 ˚A bandpass
Figure 8.5: The Ca II H+K lines of HD124570 observed at Apr. 18 2009, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 2); left:
Caii K line with a S/N of 31 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 37 electrons/pixel in 1 ˚A bandpass
measurement (S = 0.130±0.006) is, within the error, equal to the S-indices by Baliunas et al. (1995) and Hall et al. (2007). HD124570 has a rotational velocity and metallicity of vsini= (5.6±1.0) km/s (Glebocki and Stawikowski 2000) and [F e/H] = 0.07 (Holmberg
8.2 Observed template star candidates 109
Figure 8.6: The Ca II H+K lines of HD142373 observed at Aug. 13 2009, the lower curve shows the original spectrum and the upper one is the rebinned spectrum (factor 2); left:
Caii K line with a S/N of 38 electrons/pixel in 1 ˚A bandpass; right: Caii H line with a S/N of 42 electrons/pixel in 1 ˚A bandpass
et al. 2009), respectively.
The Caii H+K lines of HD124570 are shown in Fig. 8.5. The spectrum of HD124570 is a co-added spectrum of 2 single observations on Apr. 18 2009. The total exposure time was 7200 sec.
The CaiiK line is too noisy to detect any feature. In the Caii H line, one can clearly see a double peak structure in the rebinned spectrum.
It is also possible to compare the S-index with the S-index of HD89744 because these stars have a comparable colour index and evolutionary state. The S-index of HD89744 is greater than the S-index of HD124570 as is the average S-index, see Table 6.1. These objects have different rotational velocities and metallicities and these differences have an influence on the S-index. The issue is, how strong the influence on these differences at the S-index is. For this object, I come to the same conclusion as for HD89744. It is possible that this object has a very low activity level.
HD142373 is also called χ Her and part of the object list, which was used to perform the S-index calibration (Sect. 6.4.2). The average S-index is hSi = 0.147 and labelled as flat active star by Baliunas et al. (1995). In Hall et al. (2007), this star is labelled as solar-activity variable without a S-index. Nevertheless, this star was listed in the list of template candidates on the basis of the small S-index and the label for long time variables in Baliunas et al. (1995). The average S-index by Baliunas et al. (1995) and the S-index for this measurement (0.146±0.006) are equal. This object has rotational velocity and metal-licity ofvsini= (2.40±0.80) km/s (Glebocki and Stawikowski 2000) and [F e/H] =−0.50 (Holmberg et al. 2009), respectively. Furthermore, a faint X-ray radiation was detected with the ROSAT satellite. The count rate was (4.93±1.53)·10−3 ct/s (Second ROSAT PSPC Catalog 2000). In Fig. 8.6, the spectra of the Caii H+K lines are shown. This spectrum is a co-added spectrum of 2 single observations on Aug. 13 2009 with a total
exposure time of 3000 sec.
In the rebinned spectrum of the Caii K line, one can clearly see a weak double peak structure and this is a sign of activity of this star. In the CaiiH line, no double peak can be seen in the spectrum. Hence, I can also conclude for this object, it is possible that this star has a very low activity level.