A&A 392, 515-528 (2002)
DOI: 10.1051/0004-6361:20020854
E. Paunzen1,2 - G. Handler3 - W. W. Weiss1 - N. Nesvacil1 - A. Hempel4,5 - E. Romero-Colmenero3 - F. F. Vuthela3,6 - P. Reegen1 - R. R. Shobbrook7 - D. Kilkenny3
1 - Institut für Astronomie der Universität Wien,
Türkenschanzstr. 17, 1180 Wien, Austria
2 -
Zentraler Informatikdienst der Universität Wien,
Universitätsstr. 7, 1010 Wien, Austria
3 -
South African Astronomical Observatory, PO Box 9, Observatory 7935,
South Africa
4 -
Department of Physics, University of Cape Town, Private
Bag, Rondebosch 7701, South Africa
5 -
Max-Planck-Institut für Astronomie,
Königsstuhl 17, 69117 Heidelberg, Germany
6 -
Department of Physics, University of the North-West,
Private Bag X2046, Mmabatho 2735, South Africa
7 -
Research School of Astronomy and Astrophysics,
Australian National University, Canberra, ACT 0200, Australia
Received 12 April 2002 / Accepted 6 June 2002
Abstract
Generally, chemical peculiarity found for stars on the upper main
sequence excludes
Scuti type pulsation (e.g. Ap and Am stars), but
for the group of
Bootisstars it is just the opposite. This makes them very
interesting for asteroseismological investigations. The group of
Bootistype
stars comprises late B- to early F-type, Population I objects which
are basically metal weak, in particular the Fe group elements, but
with the clear exception of C, N, O and S.
The present work is a continuation of the studies by Paunzen et al. (1997,
1998), who presented first results on the pulsational characteristics of
the
Bootisstars. Since then, we have observed 22 additional objects; we
found eight new pulsators and confirmed another one. Furthermore, new
spectroscopic data (Paunzen 2001) allowed us to sort out misidentified
candidates and to add true members to the group. From 67 members
of this group, only two are not photometrically investigated yet which
makes our analysis highly representative.
We have compared our results on the pulsational behaviour of the
Bootisstars
with those of a sample of
Scuti type objects. We find that at
least 70% of all
Bootistype stars inside the classical instability strip
pulsate, and they do so with high overtone modes (Q < 0.020 d). Only
a few stars, if any, pulsate in the fundamental mode. Our photometric
results are in excellent agreement with the spectroscopic work on
high-degree nonradial pulsations by Bohlender et al. (1999). Compared to
the
Scuti stars, the cool and hot borders of the instability
strip of the
Bootisstars are shifted by about 25 mmag,
towards smaller (b-y)0.
Using published abundances and the metallicity sensitive indices of the
Geneva 7-colour and Strömgren
systems, we have derived [Z]
values which describe the surface abundance of the heavier elements for
the group members. We find that the
Period-Luminosity-Colour relation for the group of
Bootisstars is within the errors
identical with that of the normal
Scuti stars. No clear evidence
for a statistically significant metallicity term was detected.
Key words: stars - Bootis; stars - chemically peculiar; stars - early type
In this paper we present an extensive survey to analyse the pulsational
characteristics of the Bootisstars. This small group comprises late B- to
early F-type, Population I stars which are metal weak (particularly the
Fe group elements), but with the clear exception of C, N, O and S. Only a
maximum of about 2% of all objects in the relevant spectral domain are
believed to be
Bootistype stars.
Several theories were developed to explain the peculiar abundance pattern for members of this group. The most acknowledged models include diffusion as main mechanism together either with mass-loss (Michaud & Charland 1986; Charbonneau 1993) or with accretion of circumstellar material (Venn & Lambert 1990; Turcotte & Charbonneau 1993). Another two theories deal with the influence of binarity on this phenomenon (Andrievsky 1997; Faraggiana & Bonifacio 1999). Heiter (2002) and Heiter et al. (2002) also tried to explain the abundance pattern in the context of the proposed theories.
In general, chemical peculiarity inhibits
Scuti type pulsation
(e.g. for Ap and Am stars, see Kurtz 2000 for a recent discussion) but for the
group of
Bootisstars it is just the opposite. In two previous studies (Paunzen et al. 1997, 1998), we presented non-variable as well as pulsating
Bootis
stars. Since then, we have observed 22 additional objects and found eight new
pulsators and confirmed another. Furthermore, new spectroscopic data (Paunzen
2001) has allowed us to sort out misidentified candidates and to add true
members of the group.
Turcotte et al. (2000) investigated the effect of diffusion (probably the
main cause of the Bootisphenomenon) on the pulsation of stars at the upper main
sequence. Although these authors mainly investigated the theoretical
behaviour of apparently metal-rich objects, their conclusions also have an
impact for the
Bootisgroup: little direct pulsational excitation from
Fe-peak elements was found, but effects due to settling of helium along
with the enhancement of hydrogen are important. Turcotte et al. (2000)
find that, as their models of peculiar stars evolve, they become generally
pulsationally unstable near the red edge of the instability strip, whereas
the behaviour at the blue edge is mainly sensitive to the surface metal
abundance. Although the proposed models are still simplified (e.g.
treatment of convection) these preliminary results already point towards the
most important effects on the theoretical pulsational instability and
behaviour of chemically peculiar stars.
The aim of the present paper is to analyse the pulsational characteristics
of the group of Bootisstars and to test for the presence of a possible
Period-Luminosity-Colour-Metallicity relation. The latter is especially
interesting in the light of the models by Turcotte et al. (2000). The
pulsational characteristics of the
Bootisgroup (e.g. ratio of variable to
non-variable objects and distribution of pulsational constants) may help
to put tighter constraints on these models.
Since our previous works (Paunzen et al. 1997, 1998) several
then-selected group members were investigated with classification resolution
spectroscopy and found to be misclassified. These are: HD 66920, HD 79025,
HD 82573, HD 141851, HD 143148, HD 145782, HD 149303, HD 179791, HD 188164 and
HD 192424 (Paunzen 2001). In total, 65 members were selected
from the lists of Gray & Corbally (1993) and
Paunzen (2001) which contain well established as well as good candidate Bootis
type objects. Together with the
two newly discovered objects (HD 42503 and HD 213669; Sect. 2.3.1), we
have a sample of 67
Bootistype stars.
Site | Date | Telescope | Stars | Ref. |
APT (Fairborn) | 05.2001 | 0.75 | 3 | 1 |
SAAO | 04.2001 | 0.50 | 8 | 2 |
07.2001 | ||||
08.2001 | ||||
09.2001 | ||||
10.2001 | ||||
SAAO | 12.2000 | 0.75 | 9 | 3 |
01.2001 | ||||
SAAO | 08.2001 | 1.00 | 1 | 4 |
Siding Spring | 01.2002 | 0.60 | 1 | 5 |
HD | JD | hrs | mV | Spec. | Freq. | Amp. | Ref. |
[mag] | [d-1] | [mag] | |||||
13755 | 2 451 899 | 3.2 | 7.84 | ![]() |
12.50 | 0.015 | 3 |
2 451 903 | 2.5 | 16.85 | 0.007 | ||||
2 451 905 | 3.1 | ||||||
2 451 909 | 3.1 | ||||||
13602 | 8.52 | F6 | |||||
13710 | 8.32 | K5 | |||||
35242 | 2 451 900 | 2.1 | 6.35 | ![]() |
38.61 | 0.005 | 3 |
2 451 902 | 5.4 | 34.16 | 0.003 | ||||
2 451 908 | 3.3 | 41.33 | 0.003 | ||||
35134 | 6.74 | A0 | |||||
34888 | 6.78 | A5 | |||||
42503 | 2 452 291 | 4.2 | 7.45 | ![]() |
7.00 | 0.015 | 5 |
2 452 292 | 1.9 | ||||||
42058 | 6.99 | A0 | |||||
43452 | 7.71 | F5 | |||||
75654 | 2 451 898 | 3.0 | 6.38 | ![]() |
14.80 | 0.005 | 3 |
2 451 902 | 1.8 | 15.99 | 0.002 | ||||
2 451 905 | 3.1 | ||||||
2 451 906 | 1.2 | ||||||
2 451 907 | 3.8 | ||||||
2 451 909 | 3.6 | ||||||
74978 | 6.87 | A1 | |||||
75272 | 6.98 | B9.5 | |||||
111604 | 2 452 061 | 4.1 | 5.89 | ![]() |
8.77 | 0.020 | 1 |
112412 | 5.61 | F1 | |||||
110375 | 8.33 | F5 | |||||
120896 | 2 452 097 | 3.9 | 8.50 | ![]() |
17.79 | 0.010 | 2 |
121372 | 8.67 | G5 | |||||
148638 | 2 452 097 | 4.6 | 7.90 | ![]() |
16.32 | 0.016 | 2 |
2 452 123 | 5.0 | ||||||
148596 | 8.60 | F2 | |||||
148573 | 8.63 | B9 | |||||
213669 | 2 451 823 | 6.5 | 7.42 | ![]() |
15.01 | 0.023 | 2 |
2 451 826 | 1.6 | ||||||
2 451 827 | 1.1 | ||||||
211878 | 7.70 | F5 | |||||
214390 | 7.90 | F3 | |||||
290799 | 2 451 904 | 3.0 | 10.63 | ![]() |
23.53 | 0.006 | 3 |
2 451 906 | 4.8 | ||||||
37652 | 7.35 | F5 | |||||
290798 | 10.40 | A2 |
The photometric observations were performed as described by Paunzen et al. (1998) using photoelectric detectors (except for Ref. "4'', Table 1, for which a CCD was used) and (if possible) two comparison stars. A standard reduction method for dealing with dead-time, dark counts and tube drifts was applied. The sky measurements (typically one per half hour) were subtracted and differential light curves were generated. For the reduction of the CCD frames for HD 290492 the standard SAAO reduction package as well as the program MOMF (Kjeldsen & Frandsen 1992) were used. Figure 1 shows light curves of some of our variable program stars.
Frequencies and amplitudes for the variable program stars (listed in Table 2) were derived using a standard Fourier algorithm (Deeming 1975). An analysis with the Phase-Dispersion-Minimization (Stellingwerf 1978) gave essentially the same results. A star is considered to be constant, if the Fourier spectrum of the differential light curve does not contain a statistically significant peak (Paunzen et al. 1997). These objects are listed in Table 3.
![]() |
Figure 1:
Differential light curves of eight newly discovered and one
confirmed (HD 75654) pulsating ![]() |
Open with DEXTER |
The following nine stars were already known as variable. With the only exception of HD 75654 (see below), they have not been re-observed by us:
HD/BD | JD | hrs | mV | Spec. | Limit | Ref |
[mag] | [mmag] | |||||
7908 | 2 451 898 | 2.0 | 7.29 | ![]() |
0.3 | 3 |
2 451 907 | 2.3 | |||||
7629 | 7.13 | A9 | ||||
7896 | 7.95 | G6 | ||||
24472 | 2 451 900 | 2.9 | 7.09 | ![]() |
0.8 | 3 |
24616 | 6.70 | G8 | ||||
25385 | 7.40 | F0 | ||||
54272 | 2 451 908 | 2.6 | 8.80 | ![]() |
1.4 | 3 |
54692 | 8.51 | A0 | ||||
+19 622 | 8.90 | A2 | ||||
74873 | 2 451 904 | 3.5 | 5.89 | ![]() |
1.6 | 3 |
74228 | 5.65 | A3 | ||||
75108 | 8.38 | G5 | ||||
83277 | 2 451 901 | 3.5 | 8.30 | ![]() |
1.4 | 3 |
83547 | 8.62 | A0 | ||||
82709 | 8.04 | A9 | ||||
90821 | 2 452 039 | 2.0 | 9.47 | ![]() |
2.2 | 1 |
90878 | 7.82 | F8 | ||||
90748 | 8.67 | F8 | ||||
107223 | 2 452 003 | 5.2 | 7.35 | ![]() |
1.9 | 2 |
107143 | 7.87 | A1 | ||||
107265 | 8.76 | A0 | ||||
111005 | 2 452 004 | 1.9 | 7.96 | ![]() |
2.1 | 2 |
110705 | 8.36 | F0 | ||||
110989 | 8.41 | F8 | ||||
130767 | 2 452 039 | 5.5 | 6.91 | ![]() |
1.2 | 1 |
130556 | 7.84 | F1 | ||||
130396 | 7.41 | F8 | ||||
149130 | 2 452 127 | 5.6 | 8.50 | ![]() |
2.4 | 2 |
148597 | 8.25 | B9 | ||||
149471 | 8.94 | F6 | ||||
216847 | 2 452 190 | 2.9 | 7.06 | ![]() |
1.7 | 2 |
2 452 191 | 3.2 | |||||
216349 | 7.84 | K1 | ||||
217686 | 7.56 | F7 | ||||
290492 | 2 451 901 | 3.0 | 9.27 | ![]() |
1.8 | 2 |
2 452 190 | 2.2 | |||||
2 452 192 | 4.0 | |||||
290575 | 9.85 | F5 | ||||
-00 984 | 8.37 | HgMn | ||||
261904 | 2 452 190 | 2.1 | 10.20 | ![]() |
3.5 | 4 |
2 452 191 | 2.2 | |||||
261941 | 10.94 | A2 |
Five well established members of the Bootisgroup were not photometrically
investigated: HD 110411, HD 125889, HD 170680, HD 184779 and HD 198160. For
three of them (HD 110411, HD 170680 and HD 198160) photometric measurements in
the HIPPARCOS and TYCHO catalogues (ESA 1997) were found. Since these
observations are not optimal to find
Scuti type pulsation, only a
rough estimate for variability can be made. We find a level of non-variability
based on the HIPPARCOS photometry of 3 mmag for HD 110411 and HD 170680, and
4 mmag for HD 198160. In fact, HD 110411 was suspected as variable by
Bartolini et al. (1980a), but Antonello & Mantegazza (1982) concluded that
there is no evidence for periodic terms in the light curve: different
oscillation modes may be excited occasionally and then be damped again. We
therefore treat this star as being constant within a limit of 3 mmag.
Consequently, the other two objects (HD 125889 and HD 184779) were not
considered in the following analysis.
In the following sections we describe special properties of some individual stars in more detail.
These two objects were suspected
Scuti type pulsators based on
HIPPARCOS photometry (Handler 2002). Handler (1999) presented Strömgren
photometry which puts these stars well within the typical area of
the
Bootisobjects in a
versus (b-y) diagram
(Paunzen et al. 1998). Our photometric measurements confirmed the
pulsation.
We have performed additional spectroscopic observations to establish the nature
of these stars. These observations were done on the 1.9 m telescope at SAAO in
the night of 03./04.10.2000. The Grating Spectrograph with the SITe CCD
together with the 600 lines mm-1 grating resulted in a useful wavelength
range of 1600 Å, a resolution of 2 Å and a signal-to-noise ratio of
about 200. The wavelength calibration was done with the help of a CuAr lamp
within standard IRAF routines. The classification was done within the system
described by Paunzen (2001). Both objects are very good Bootiscandidates, with
derived spectral types of A2 V (
Boo) and kA1hF0mA1 V
Boo for HD 42503 and HD 213669, respectively.
The notation of the spectral classification is according to Gray (1988) where
k stands for the classification of the Caii K line, h for the hydrogen
lines and m for the appearance of the metallic-line spectrum compared to MK standards.
We therefore included them in our
sample. Figure 2 shows their spectra together with those of two
well established
Bootisstars (HD 107233 and HD 198160; taken from Paunzen 2001)
which exhibit similar spectral characteristics. However, we note that a final
decision on their group membership has to be made after a detailed
determination of their chemical abundances (especially of C, N, O and S) which was not done so far.
Both stars are
Scuti type pulsators and were reported as well
established members of the group by Gray (1988) and Paunzen & Gray
(1997). However, both objects are spectroscopic binary systems (Faraggiana &
Bonifacio 1999; Iliev et al. 2001). The published information on these stars
does not allow us to decide whether they are true
Bootistype objects, thus we
have not included either of them in our sample.
We have re-observed this object because the upper limit for non-variability given by Paunzen et al. (1997) was very high (9.4 mmag). Our new observations showed no variability within a limit of 1.6 mmag.
This object exhibits a peculiar behaviour which we have, so far, been unable to understand. During our first short observing run (on 06/07 July 2001), its magnitude and colour were consistent with their standard values from the literature (b = 7.85, v-b = 0.222), and marginal evidence for pulsational variability was found. However, when we attempted to re-observe the star on 05/06 August 2001, it appeared much fainter and redder than in the previous month.
HD | (b-y)0 | log
![]() |
log g | v sin i | [Z] | MV | MB | log
![]() |
log P | Q |
[mag] | [dex] | [dex] | [km s-1] | [dex] | [mag] | [mag] | [dex] | [d] | ||
6870 | 0.164 | 3.865(6) | 3.84(11) | 165 | -1.03(20) | +2.29(42) | +2.20 | 1.02(17) | -1.19 | 0.023 |
11413 | 0.104 | 3.899(7) | 3.91(21) | 125 | -1.17(10) | +1.49(10) | +1.36 | 1.35(4) | -1.38 | 0.014 |
13755 | 0.181 | 3.850(10) | 3.26(10) | - | -0.75(30) | +0.93(10) | +0.83 | 1.57(4) | -1.12 | 0.010 |
15165 | 0.189 | 3.846(12) | 3.23(10) | 90 | -1.15(17) | +1.12(16) | +1.01 | 1.50(6) | -0.87 | 0.017 |
30422 | 0.098 | 3.896(6) | 4.00(20) | 135 | -1.50(20) | +2.35(2) | +2.23 | 1.01(1) | -1.68 | 0.010 |
35242 | 0.058 | 3.916(5) | 3.90(14) | 90 | -1.40(20) | +1.75(22) | +1.60 | 1.26(9) | -1.58 | 0.010 |
42503 | 0.110 | 3.885(16) | 3.10(10) | - | -0.83(20) | -0.03(4) | -0.14 | 1.96(2) | -0.85 | 0.013 |
75654 | 0.158 | 3.866(6) | 3.77(11) | 45 | -0.91(11) | +1.83(12) | +1.74 | 1.20(5) | -1.18 | 0.019 |
83041 | 0.185 | 3.852(13) | 3.76(20) | 95 | -1.03(8) | +1.70(30) | +1.60 | 1.26(12) | -1.18 | 0.018 |
84948B![]() |
0.196 | 3.833(13) | 3.70(15) | 55 | -0.82(19) | +1.63(30) | +1.75 | 1.20(12) | -1.11 | 0.020 |
87271 | 0.149 | 3.876(13) | 3.43(10) | - | -1.11(30) | +1.02(8) | +0.92 | 1.53(3) | -1.27 | 0.009 |
102541 | 0.141 | 3.885(10) | 4.22(16) | - | -0.95(20) | +2.34(21) | +2.23 | 1.01(9) | -1.30 | 0.029 |
105058 | 0.127 | 3.889(10) | 3.77(30) | 140 | -0.82(7) | +0.86(30) | +0.75 | 1.60(12) | -1.40 | 0.010 |
105759 | 0.142 | 3.874(6) | 3.65(10) | 120 | -0.92(30) | +1.35(21) | +1.25 | 1.40(8) | -1.20 | 0.015 |
109738![]() |
0.144 | 3.881(8) | 3.90(13) | - | -1.02(20) | +1.85(30) | +1.75 | 1.20(12) | -1.49 | 0.012 |
110377 | 0.120 | 3.888(5) | 3.97(14) | 170 | -0.83(20) | +1.96(11) | +1.85 | 1.16(5) | -1.45 | 0.014 |
111604 | 0.112 | 3.890(8) | 3.61(25) | 180 | -1.04(3) | +0.48(7) | +0.37 | 1.75(3) | -0.94 | 0.022 |
120500 | 0.064 | 3.915(4) | 3.86(10) | 125 | -0.73(14) | +0.85(34) | +0.70 | 1.62(13) | -1.32 | 0.014 |
120896![]() |
0.166 | 3.861(5) | 3.76(10) | - | -0.82(30) | +1.90(30) | +1.81 | 1.18(12) | -1.25 | 0.016 |
125162 | 0.042 | 3.941(8) | 4.07(9) | 115 | -1.61(24) | +1.71(23) | +1.54 | 1.28(9) | -1.64 | 0.011 |
142703 | 0.177 | 3.861(9) | 3.93(12) | 100 | -1.32(5) | +2.41(12) | +2.32 | 0.97(5) | -1.43 | 0.015 |
142944![]() |
0.198 | 3.845(8) | 3.19(4) | 180 | -0.91(38) | +0.80(30) | +0.69 | 1.62(12) | -0.85 | 0.016 |
148638![]() |
0.106 | 3.882(13) | 3.39(10) | - | -0.80(30) | +0.33(30) | +0.23 | 1.81(12) | -1.21 | 0.009 |
153747 | 0.068 | 3.914(5) | 3.70(24) | - | -0.86(20) | +1.24(30) | +1.09 | 1.46(12) | -1.31 | 0.013 |
168740 | 0.128 | 3.883(5) | 3.88(14) | 145 | -0.91(8) | +1.82(2) | +1.72 | 1.21(1) | -1.44 | 0.013 |
168947![]() |
0.145 | 3.878(11) | 3.67(10) | - | -0.74(20) | +1.28(30) | +1.18 | 1.43(12) | -1.23 | 0.014 |
183324 | 0.032 | 3.952(10) | 4.13(4) | 90 | -1.47(6) | +1.64(42) | +1.44 | 1.32(17) | -1.68 | 0.011 |
191850![]() |
0.163 | 3.869(9) | 3.61(10) | - | -0.96(30) | +1.50(30) | +1.41 | 1.34(12) | -1.13 | 0.017 |
192640 | 0.095 | 3.900(5) | 3.95(18) | 80 | -1.46(8) | +1.84(2) | +1.71 | 1.22(1) | -1.55 | 0.011 |
210111 | 0.136 | 3.878(7) | 3.84(15) | 55 | -1.04(20) | +1.76(15) | +1.66 | 1.23(6) | -1.36 | 0.014 |
213669 | 0.155 | 3.872(8) | 3.82(17) | - | -0.93(20) | +1.79(21) | +1.69 | 1.22(8) | -1.18 | 0.021 |
221756 | 0.046 | 3.930(10) | 3.90(3) | 105 | -0.71(3) | +1.16(16) | +1.00 | 1.50(6) | -1.36 | 0.015 |
290799![]() |
0.114 | 3.889(5) | 4.18(10) | 70 | -0.82(26) | +2.62(30) | +2.51 | 0.90(12) | -1.37 | 0.025 |
HD | (b-y)0 | log
![]() |
log g | v sin i | [Z] | MV | MB | log
![]() |
log P | Q |
[mag] | [dex] | [dex] | [km s-1] | [dex] | [mag] | [mag] | [dex] | [d] | ||
432 | 0.211 | 3.841(4) | 3.44(7) | 70 | +0.45 | 1.19(29) | 1.08 | 1.47(11) | -1.00 | 0.017 |
3112 | 0.127 | 3.883(5) | 3.59(9) | 80 | +0.28 | 0.54(84) | 0.44 | 1.73(34) | -1.31 | 0.009 |
4490 | 0.156 | 3.867(3) | 3.55(9) | 180 | +0.22 | 0.92(15) | 0.83 | 1.57(6) | -0.98 | 0.019 |
4849 | 0.168 | 3.862(2) | 3.78(8) | - | +0.52 | 1.65(30) | 1.56 | 1.27(12) | -1.26 | 0.016 |
7312 | 0.169 | 3.861(3) | 3.79(6) | - | +0.24 | 1.71(28) | 1.62 | 1.25(11) | -1.38 | 0.012 |
8511 | 0.134 | 3.880(4) | 3.96(6) | 190 | -0.06 | 2.04(1) | 1.94 | 1.12(1) | -1.16 | 0.027 |
8781 | 0.213 | 3.838(6) | 3.46(6) | - | -0.03 | 1.57(18) | 1.46 | 1.32(7) | -0.95 | 0.020 |
9065 | 0.200 | 3.844(6) | 3.46(6) | - | -0.14 | 1.72(21) | 1.61 | 1.26(8) | -1.02 | 0.018 |
9100 | 0.087 | 3.899(8) | 3.53(22) | 120 | -0.34 | 0.43(28) | 0.30 | 1.78(11) | -0.87 | 0.024 |
11522 | 0.162 | 3.861(5) | 3.41(6) | 120 | -0.04 | 0.76(13) | 0.67 | 1.63(5) | -1.04 | 0.014 |
15550 | 0.152 | 3.871(3) | 3.84(6) | 170 | +0.13 | 1.89(1) | 1.80 | 1.18(1) | -1.17 | 0.022 |
15634 | 0.179 | 3.858(2) | 3.81(7) | 140 | +0.28 | 1.57(50) | 1.48 | 1.31(20) | -1.01 | 0.028 |
17093 | 0.133 | 3.883(8) | 4.04(11) | 75 | -0.10 | 2.22(4) | 2.12 | 1.05(2) | -1.45 | 0.016 |
19279 | 0.063 | 3.913(8) | 3.76(17) | 285 | -0.16 | 1.69(61) | 1.54 | 1.28(25) | -1.16 | 0.022 |
23728 | 0.178 | 3.859(5) | 3.70(16) | 105 | -0.21 | 1.62(15) | 1.53 | 1.29(6) | -1.00 | 0.025 |
24809 | 0.119 | 3.890(10) | 4.26(20) | 130 | -0.36 | 2.51(7) | 2.40 | 0.94(3) | -1.26 | 0.035 |
24832 | 0.158 | 3.865(4) | 3.69(13) | 140 | +0.12 | 1.12(30) | 1.03 | 1.49(12) | -0.81 | 0.035 |
26574 | 0.196 | 3.847(4) | 3.49(12) | 100 | +0.62 | 1.22(38) | 1.11 | 1.46(15) | -1.13 | 0.013 |
27397 | 0.166 | 3.864(3) | 3.96(5) | 100 | +0.22 | 2.30(5) | 2.21 | 1.02(2) | -1.26 | 0.022 |
27459 | 0.123 | 3.884(5) | 3.96(13) | 75 | +0.25 | 1.92(21) | 1.82 | 1.17(9) | -1.44 | 0.014 |
28024 | 0.159 | 3.865(7) | 3.40(18) | 210 | +0.22 | 0.77(24) | 0.68 | 1.63(9) | -0.83 | 0.022 |
28319 | 0.093 | 3.901(9) | 3.70(12) | 80 | +0.16 | 0.32(78) | 0.19 | 1.82(31) | -1.12 | 0.016 |
28910 | 0.139 | 3.877(4) | 3.97(5) | 125 | +0.19 | 1.58(75) | 1.48 | 1.31(30) | -1.17 | 0.024 |
30780 | 0.114 | 3.887(3) | 3.87(11) | 150 | +0.23 | 1.41(50) | 1.30 | 1.38(20) | -1.38 | 0.013 |
32846 | 0.189 | 3.845(9) | 3.37(10) | - | -0.19 | 1.16(5) | 1.05 | 1.48(2) | -0.87 | 0.021 |
50018 | 0.217 | 3.836(6) | 3.35(10) | 135 | +0.78 | 0.49(1.03) | 0.37 | 1.75(41) | -0.81 | 0.019 |
57167 | 0.214 | 3.844(2) | 3.97(3) | 100 | +0.18 | 2.49(15) | 2.38 | 0.95(6) | -1.33 | 0.019 |
71496 | 0.133 | 3.878(4) | 3.61(8) | 130 | +0.41 | 1.18(10) | 1.08 | 1.47(4) | -1.02 | 0.021 |
71935 | 0.140 | 3.872(4) | 3.67(9) | 160 | +0.32 | 1.14(20) | 1.04 | 1.49(8) | -1.15 | 0.016 |
73575 | 0.137 | 3.874(5) | 3.41(12) | 150 | +0.32 | 0.38(21) | 0.28 | 1.79(8) | -0.99 | 0.015 |
74050 | 0.106 | 3.892(7) | 3.85(16) | 145 | +0.25 | 1.71(44) | 1.59 | 1.26(18) | -1.24 | 0.019 |
84999 | 0.192 | 3.851(4) | 3.41(8) | 110 | +0.13 | 1.09(27) | 0.99 | 1.50(11) | -0.88 | 0.021 |
88824 | 0.153 | 3.870(2) | 3.83(10) | 235 | +0.08 | 1.76(2) | 1.67 | 1.23(1) | -0.90 | 0.039 |
94985 | 0.088 | 3.903(9) | 3.62(5) | - | -0.11 | 0.82(16) | 0.69 | 1.62(6) | -0.82 | 0.032 |
103313 | 0.110 | 3.889(4) | 3.67(8) | 70 | +0.24 | 0.79(36) | 0.68 | 1.63(14) | -1.10 | 0.017 |
104036 | 0.086 | 3.899(7) | 4.09(14) | - | +0.01 | 1.67(40) | 1.54 | 1.28(16) | -1.52 | 0.013 |
107131 | 0.097 | 3.897(5) | 4.03(20) | 185 | -0.08 | 1.91(25) | 1.78 | 1.19(10) | -1.18 | 0.029 |
107904 | 0.224 | 3.837(6) | 3.20(12) | 115 | +0.68 | 0.83(15) | 0.72 | 1.61(6) | -0.93 | 0.013 |
109585 | 0.208 | 3.841(4) | 3.59(10) | 80 | +0.16 | 1.80(18) | 1.69 | 1.22(7) | -1.09 | 0.018 |
115308 | 0.199 | 3.846(6) | 3.36(8) | 75 | +0.06 | 1.16(2) | 1.05 | 1.48(1) | -0.93 | 0.017 |
117661 | 0.095 | 3.900(4) | 3.95(11) | 55 | +0.14 | 1.70(12) | 1.57 | 1.27(5) | -1.37 | 0.016 |
124675 | 0.111 | 3.884(6) | 3.67(17) | 120 | -0.11 | 1.02(29) | 0.91 | 1.54(12) | -1.19 | 0.015 |
125161 | 0.128 | 3.885(8) | 4.10(19) | 135 | +0.08 | 2.40(14) | 2.29 | 0.98(5) | -1.58 | 0.013 |
127762 | 0.112 | 3.890(3) | 3.69(12) | 130 | +0.02 | 0.94(2) | 0.83 | 1.57(1) | -1.14 | 0.017 |
127929 | 0.143 | 3.876(3) | 3.65(11) | 70 | +0.00 | 0.80(29) | 0.70 | 1.62(12) | -1.06 | 0.018 |
138918 | 0.146 | 3.870(5) | 3.77(23) | 85 | +0.16 | 0.19(1.13) | 0.10 | 1.86(45) | -0.81 | 0.032 |
143466 | 0.177 | 3.863(5) | 3.92(15) | 145 | +0.24 | 2.29(8) | 2.20 | 1.02(3) | -1.12 | 0.029 |
152569 | 0.160 | 3.864(3) | 3.81(13) | 195 | +0.16 | 1.83(4) | 1.74 | 1.21(2) | -1.12 | 0.023 |
155514 | 0.119 | 3.886(6) | 3.90(16) | 175 | +0.08 | 1.49(17) | 1.38 | 1.35(7) | -1.05 | 0.029 |
171369 | 0.159 | 3.863(3) | 3.79(8) | 80 | +0.05 | 1.64(20) | 1.55 | 1.28(8) | -1.04 | 0.026 |
176723 | 0.200 | 3.848(3) | 3.62(9) | 265 | +0.10 | 1.66(19) | 1.56 | 1.27(8) | -0.87 | 0.031 |
177392 | 0.168 | 3.861(6) | 3.54(16) | 140 | +0.15 | 0.96(10) | 0.87 | 1.55(4) | -0.96 | 0.020 |
177482 | 0.161 | 3.862(5) | 3.45(8) | 145 | +0.26 | 0.86(14) | 0.77 | 1.59(6) | -1.01 | 0.016 |
181333 | 0.138 | 3.877(4) | 3.53(6) | 55 | +0.38 | 0.47(47) | 0.37 | 1.75(19) | -0.82 | 0.025 |
182475 | 0.194 | 3.850(3) | 3.63(14) | 130 | +0.32 | 1.61(47) | 1.51 | 1.30(19) | -1.11 | 0.018 |
HD | (b-y)0 | log
![]() |
log g | v sin i | [Z] | MV | MB | log
![]() |
log P | Q |
[mag] | [dex] | [dex] | [km s-1] | [dex] | [mag] | [mag] | [dex] | [d] | ||
185139 | 0.157 | 3.869(2) | 3.80(7) | - | +0.29 | 1.38(51) | 1.29 | 1.39(20) | -1.19 | 0.018 |
186786 | 0.181 | 3.856(2) | 3.86(8) | - | +0.19 | 2.09(3) | 2.00 | 1.10(1) | -1.10 | 0.027 |
188520 | 0.123 | 3.885(7) | 4.05(15) | - | +0.03 | 2.19(19) | 2.08 | 1.07(8) | -1.26 | 0.025 |
199124 | 0.167 | 3.859(3) | 3.74(8) | 150 | -0.12 | 1.89(13) | 1.80 | 1.18(5) | -1.00 | 0.028 |
199908 | 0.192 | 3.848(4) | 3.42(7) | 60 | +0.27 | 1.23(21) | 1.13 | 1.45(8) | -1.10 | 0.013 |
206553 | 0.171 | 3.859(4) | 3.70(15) | - | +0.20 | 1.46(2) | 1.37 | 1.35(1) | -1.20 | 0.016 |
208435 | 0.198 | 3.844(5) | 3.26(8) | - | +0.36 | 0.67(43) | 0.56 | 1.68(17) | -0.83 | 0.017 |
211336 | 0.170 | 3.862(3) | 3.90(7) | 90 | +0.17 | 2.12(2) | 2.03 | 1.09(1) | -1.39 | 0.015 |
214441 | 0.205 | 3.847(4) | 3.55(11) | - | +0.45 | 1.28(59) | 1.18 | 1.43(23) | -0.90 | 0.024 |
215874 | 0.163 | 3.863(4) | 3.48(5) | 100 | +0.23 | 0.88(20) | 0.79 | 1.58(8) | -1.06 | 0.015 |
217236 | 0.152 | 3.868(4) | 3.52(8) | 100 | +0.22 | 0.51(59) | 0.42 | 1.73(24) | -0.90 | 0.020 |
219891 | 0.076 | 3.902(8) | 3.77(15) | 165 | -0.02 | 0.80(6) | 0.67 | 1.63(3) | -1.00 | 0.025 |
220061 | 0.100 | 3.882(17) | 3.51(2) | 140 | +0.04 | 0.95(14) | 0.85 | 1.56(6) | -1.27 | 0.010 |
223781 | 0.098 | 3.897(4) | 3.92(12) | 165 | -0.20 | 1.47(8) | 1.34 | 1.37(3) | -1.22 | 0.021 |
![]() |
Figure 2:
Classification resolution spectra of the two newly discovered
![]() ![]() ![]() ![]() ![]() |
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Consequently, we double-checked its correct identification and re-examined the literature. We found no evidence for a misidentification or previous peculiar behaviour. We obtained a 3 hr light curve on the night of 06/07 August 2001, where the object appeared as a star of b = 10.67 and v-b = 1.17. These observations are consistent with an eclipse by a late K subgiant companion. However, the evolutionary history of such a system would require the binary to be close, and no other possible eclipses have yet been reported.
Paunzen et al. (1998) reported this star as constant with an upper limit of 10 mmag in Geneva V1. Our new observations show the star to be pulsating with a frequency of 23.53 d-1 and an amplitude of 6 mmag in Strömgren b.
In this section we describe the calibration procedures within various photometric systems and derivation of the basic stellar parameters required to analyse the pulsational characteristics of these stars, such as the effective temperature, surface gravity and the luminosity.
The required standard photometric colours were taken from the General Catalogue of Photometric Data (GCPD; http://obswww.unige.ch/gcpd/) as well as the HIPPARCOS and TYCHO databases (ESA 1997). If available, averaged and weighted mean values were used.
The following calibrations for the individual photometric systems were used to derive effective temperatures and surface gravities:
Normally, the reddening for objects within the solar neighborhood is estimated
using photometric calibrations in the Strömgren
system
(Strömgren 1966; Crawford 1979; Hilditch et al. 1983). These calibrations are
not very reliable for stars with spectral types from A0 to A3 (Gerbaldi et al. 1999), mainly because for these stars, the reddening free parameter
is no longer a temperature indicator alone but is also sensitive to the
luminosity. From the photometry we find that two of our pulsating (HD 125162
and HD 183324) and nine constant (HD 23392, HD 31295, HD 36726, HD 74873,
HD 110411, HD 130767, HD 170680, HD 261904 and HD 294253) program stars fall
into A0 to A3 spectral region.
An independent way to derive the interstellar reddening is to use galactic
reddening maps, which are derived from open clusters as well as from galactic
field stars. Several different models have been published in the literature
(Arenou et al. 1992; Hakkila et al. 1997). Chen et al. (1998) compared the
results from Arenou et al. (1992) and those derived from the HIPPARCOS
measurements and found an overestimation of previously published results
from Arenou et al. (1992) for
distances less than 500 pc. They consequently proposed a new model for
galactic latitudes of 10
,
but otherwise find excellent agreement
with the model by Sandage (1972). We have used the proposed model by Chen et al. (1998) to derive the interstellar reddening for all program stars. The
values from the calibration of the Strömgren
and the model by
Chen et al. (1998) are in very good agreement. To minimize possible
inconsistencies we have averaged the values from both approaches.
In Table 7, we compare our photometrically derived effective
temperatures and surface gravities of 29 program stars from this work (TW) with those of Table 1 from Heiter et al. (2002), which contains averaged values from the literature
based on spectroscopic analyses. The average difference for the effective
temperature is
=
(Lit.) -
(TW) = +72(210) K, and for the average surface gravity
=
(Lit.) -
(TW) = +0.07(24) dex. We note that
there are some stars for which the spectroscopically derived values are
significantly different from the photometrically derived ones (e.g. HD 106223
and HD 107233). These cases were already extensively discussed by Heiter et al. (2002). Although such deviating cases obviously exist, we believe that our
calibration method is consistent and therefore suitable for a statistical
analysis.
For all program stars photometrically calibrated absolute magnitudes
(assuming that all objects are single) were estimated
with an error
of 0.3 mag. As an independent source we have taken the HIPPARCOS
parallaxes (if available) to derive absolute magnitudes using the
visual magnitude and reddening. Since we also corrected for the
Lutz-Kelker effect (Koen 1992) which is only possible for
parallax measurements with an absolute error of
[
] < 0.175 it seriously limits the useful data.
Oudmaijer et al. (1998) showed that this effect
has to be taken into account if individual absolute magnitudes
are calculated using HIPPARCOS parallaxes. Stars without measurements
satisfying [
] < 0.175 are marked with an asterisk in
Tables 4 and 6 (20 stars in total).
For the other 45 objects we are able to derive weighted means
(taking the errors as weights, i.e. a larger error is a lower weight)
for the absolute magnitude using the values from the photometric calibration
procedure and the conversion of the HIPPARCOS parallax measurements. For
the remaining 20 stars only photometrically calibrated absolute magnitudes
are available.
We then calculated luminosities (log
/
)
using the absolute bolometric
magnitude of the Sun
= 4.75 mag (Cayrel de Strobel 1996)
and bolometric corrections taken from Drilling & Landolt (2000).
For HD 84948B we have used the astrophysical parameters listed by Iliev et al. (2002; Table 1). This is an evolved spectroscopic binary system which
contains two similar Bootiscomponents; Iliev et al. (2002) have taken
the binary nature into account.
Individual abundances and projected
rotational velocities for members of the Bootisgroup were
published by Uesugi & Fukuda (1982), Venn & Lambert (1990), Stürenburg
(1993), Abt & Morrell (1995), Holweger & Rentzsch-Holm (1995), Chernyshova et al. (1998), Heiter et al. (1998), Paunzen et al. (1999a,b), Kamp et al. (2001),
Solano et al. (2001), Heiter (2002) and Andrievsky et al. (2002). The
individual values were weighted (if possible) with the errors listed in the
references and averaged.
The published abundances do not allow an investigation of the correlation of individual
abundances of different elements (which have different diffusion properties)
with the pulsational period. It is well known that the typical abundance
pattern of Bootisstars is characterized by moderate to strong underabundances of
elements heavier than C, N, O and S. To get an overall estimate of the
(surface) abundance we have applied the following method:
![]() |
Figure 3: The histogram of our upper levels for non-variability. See text for details. |
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![]() |
Figure 4:
The log
![]() ![]() ![]() |
Open with DEXTER |
![]() |
Figure 5:
The log
![]() ![]() ![]() ![]() ![]() |
Open with DEXTER |
Besides two objects (HD 125889 and HD 184779),
all members of the Bootisgroup were photometrically
investigated. All previously published results were taken from Paunzen et al. (1997, 1998) as well as from the references quoted in Sect. 3.
Of these
65 stars, 32 are presumed to be constant whereas 33 are pulsating. The upper
limits for non-variability, which are below 5 mmag for all but three stars
(HD 31925, HD 91130 and HD 294253), are shown in Fig. 3.
In order to investigate the pulsational characteristics of the Bootisstars as a
group, we compare them with those of "normal''
Scuti variables.
The next subsection describes the compilation of
the latter sample.
As a basis we have used the catalogue of Rodriguez et al. (2000). From this sample, stars have been rejected following these criteria:
First of all, we have investigated the location of all Bootisstars within
the log
versus log
and MV versus (b-y)0 diagrams (Fig. 4).
The borders of the classical instability strip are taken from Breger (1995).
There are several conclusions from this figure:
![]() |
Figure 6:
The histograms of the pulsational constant Q for
the selected ![]() ![]() |
Open with DEXTER |
As a next step towards analyzing the
pulsational characteristics we have calculated the pulsation constants
given by
![]() |
Figure 7:
Correlation of (b-y)0, the absolute magnitude and metallicity with
log P for all ![]() |
Open with DEXTER |
HD | (b-y)0 | log
![]() |
MV | log
![]() |
[mag] | [mag] | |||
319 | +0.078 | 3.904(7) | 1.27(19) | 1.45(8) |
7908 | +0.192 | 3.854(5) | 2.60(18) | 0.90(7) |
23392![]() |
-0.008 | 3.991(12) | 1.43(30) | 1.45(12) |
24472 | +0.213 | 3.842(8) | 2.14(11) | 1.09(5) |
31295 | +0.029 | 3.950(9) | 1.66(22) | 1.32(9) |
36726![]() |
-0.004 | 3.978(10) | 1.74(30) | 1.32(12) |
54272![]() |
+0.214 | 3.846(13) | 2.33(30) | 1.01(12) |
74873 | +0.046 | 3.940(12) | 1.82(1) | 1.24(1) |
81290![]() |
+0.225 | 3.839(13) | 1.85(30) | 1.20(12) |
83277 | +0.196 | 3.845(12) | 1.49(29) | 1.35(12) |
84123 | +0.226 | 3.847(11) | 1.58(15) | 1.31(6) |
90821![]() |
+0.065 | 3.913(4) | 0.74(30) | 1.66(12) |
91130 | +0.073 | 3.910(5) | 1.36(26) | 1.42(11) |
101108![]() |
+0.113 | 3.893(4) | 1.33(30) | 1.42(12) |
106223 | +0.225 | 3.836(16) | 1.83(45) | 1.22(18) |
107233 | +0.181 | 3.861(9) | 2.64(13) | 0.88(5) |
110411 | +0.029 | 3.951(10) | 1.90(28) | 1.22(11) |
111005 | +0.222 | 3.836(4) | 1.76(53) | 1.24(21) |
130767 | +0.002 | 3.964(10) | 1.27(2) | 1.48(1) |
149130![]() |
+0.208 | 3.842(6) | 1.51(30) | 1.34(12) |
154153 | +0.194 | 3.848(7) | 1.86(29) | 1.19(11) |
156954 | +0.188 | 3.853(6) | 2.81(33) | 0.82(13) |
170680 | -0.013 | 3.993(11) | 0.83(23) | 1.70(9) |
175445 | +0.030 | 3.930(10) | 1.08(27) | 1.53(11) |
193256![]() |
+0.101 | 3.889(5) | 1.08(30) | 1.51(12) |
193281![]() |
+0.072 | 3.905(6) | 0.41(30) | 1.79(12) |
198160 | +0.103 | 3.896(7) | 1.47(41) | 1.36(16) |
204041 | +0.086 | 3.902(5) | 1.75(18) | 1.25(7) |
216847 | +0.155 | 3.867(5) | 0.93(24) | 1.56(10) |
261904![]() |
+0.005 | 3.974(9) | 1.33(30) | 1.48(12) |
290492![]() |
+0.084 | 3.908(8) | 2.04(30) | 1.14(12) |
294253![]() |
-0.038 | 4.027(6) | 1.32(30) | 1.58(12) |
Literature | This work | |||
HD |
![]() |
log g |
![]() |
log g |
![]() |
![]() |
|||
319 | 8100 | 3.8 | 8020(135) | 3.74(8) |
11413 | 7900 | 3.8 | 7925(124) | 3.91(21) |
15165 | 7200 | 3.7 | 7010(167) | 3.23(10) |
31295 | 8800 | 4.2 | 8920(177) | 4.20(1) |
74873 | 8900 | 4.6 | 8700(245) | 4.21(11) |
75654 | 7250 | 3.8 | 7350(104) | 3.77(11) |
81290 | 6780 | 3.5 | 6895(214) | 3.82(28) |
84123 | 6800 | 3.5 | 7025(145) | 3.73(17) |
101108 | 7900 | 4.1 | 7810(90) | 3.90(18) |
105759 | 8000 | 4.0 | 7485(102) | 3.65(10) |
106223 | 7000 | 4.3 | 6855(247) | 3.49(18) |
107233 | 7000 | 3.8 | 7265(143) | 4.03(10) |
109738 | 7575 | 3.9 | 7610(145) | 3.90(13) |
110411 | 9100 | 4.5 | 8930(206) | 4.14(14) |
111005 | 7410 | 3.8 | 6860(66) | 3.72(10) |
125162 | 8650 | 4.0 | 8720(156) | 4.07(9) |
142703 | 7100 | 3.9 | 7265(150) | 3.93(12) |
156954 | 6990 | 4.1 | 7130(93) | 4.04(13) |
168740 | 7700 | 3.7 | 7630(81) | 3.88(14) |
170680 | 10000 | 4.1 | 9840(248) | 4.15(6) |
183324 | 9300 | 4.3 | 8950(204) | 4.13(4) |
192640 | 7960 | 4.0 | 7940(96) | 3.95(18) |
193256 | 7800 | 3.7 | 7740(94) | 3.69(17) |
193281 | 8070 | 3.6 | 8035(115) | 3.54(4) |
198160 | 7900 | 4.0 | 7870(129) | 3.99(9) |
204041 | 8100 | 4.1 | 7980(97) | 3.97(8) |
210111 | 7530 | 3.8 | 7550(123) | 3.84(15) |
221756 | 9010 | 4.0 | 8510(188) | 3.90(3) |
The distribution of the Q-values for the Bootistype stars is different from
that of the
Scuti type sample (Fig. 6, upper panel) at a
99.9% level (derived from a t-test).
We also noticed four pulsators (HD 15165, HD 42503, HD 111604 and HD 142994) that have considerably longer periods (log P > -0.94 corresponding to P < 8.7 d-1) than the rest of our sample. They do, however, show a similar behaviour to the remaining group members.
A Period-Luminosity-Metallicity relation was found for Population II type variables such as RR Lyrae and SX Phoenicis stars as well as Cepheids (Nemec et al. 1994). These objects pulsate in the radial fundamental, first and second overtone modes. The dependence of the pulsational period on the metallicity is purely evolutionary, i.e. older objects exhibit a lower overall abundance and a different pulsational period. The Period-Luminosity-Metallicity relation serves as a distance indicator widely used for extragalactic objects.
The situation for Bootisstars is very different. All evidence
indicates that we find only peculiar
surface abundances whereas the overall abundance of the stars is solar,
i.e. these stars are true Population I objects.
The conclusion that
Bootisstars are true Population I objects is based on
their galactic space motions (Faraggiana & Bonifacio 1999) combined
with their location in the Hertzsprung-Russell-diagram (Fig. 4).
With the exception of the SX Phe stars, Population II type objects are
located at much higher absolute magnitudes and thus luminosities than
found for the
Bootisgroup. However, the space motions of SX Phe stars are
inconsistent with Population I, which facilitates an easy separation
from
Bootisstars.
To examine the presence of a PLCZ relation, the following basic approach
was chosen:
coeff. | value | F | value | F |
[%] | [%] | |||
![]() |
||||
a | -1.25(9) | <0.01 | -1.41(9) | <0.01 |
b(b-y)0 | +3.01(41) | <0.01 | +2.71(46) | <0.01 |
c(MB) | -0.20(3) | <0.01 | -0.19(3) | <0.01 |
d[Z] | +0.14(6) | 13.20 | -0.06(17) | 74.49 |
![]() |
||||
a | -1.17(6) | <0.01 | ||
b(b-y)0 | +2.71(43) | <0.01 | ||
c(MB) | -0.23(3) | <0.01 | ||
d[Z] | -0.28(7) | <0.01 |
To investigate whether the [Z] term is indeed significant, a plot
[log P -
2.86(b-y)0 + 0.195(MB)] versus [Z] was drawn
(Fig. 8). The coefficients for (b-y)0 and MB are the
mean values from Table 8 and are consistent within the errors for both
the Scuti and
Bootissamples. Figure 8 shows that both samples
exhibit a trend with [Z] (with an offset of about 1 dex).
Whereas the [Z] term is statistically significant
for the selected sample of
Scuti stars, it is caused by only six
Bootis
stars with strong underabundances (HD 30422, HD 35242, HD 125162, HD 142703,
HD 183324 and HD 192640) and vanishes after excluding them.
We have also tested the sample for possible correlations of the [Z] term by excluding other
data points. We find no other
selection criteria of objects by means of a physical explanation, only "suitable''
discarding would yield a clear correlation. This implies that
the peculiar abundances do not affect the pulsational period for the group of
Bootistype stars. However, we find within the errors no difference of the PLC
relation for the
Bootisand
Scuti type stars.
We have investigated the pulsational characteristics of a group of Bootis
stars and compared it to a sample of
Scuti pulsators. The latter
was chosen such that it matches our program stars within the global
astrophysical parameters. The following properties of the
Bootisstars are
different from those of the
Scuti pulsators:
![]() |
Figure 8:
Correlation of [Z] for the ![]() ![]() |
Open with DEXTER |
Acknowledgements
This work benefitted from the Fonds zur Förderung der wissenschaftlichen Forschung, project P14984. ERC would like to thank D. Romero, E. Colmenero and S. Potter for their support. Use was made of the SIMBAD database, operated at CDS, Strasbourg, France and the GCPD database, operated at the Institute of Astronomy of the University of Lausanne. We are also indebted to the committees of the SAAO, Siding Spring and Fairborn Observatory who granted observing time.