3 Abundance analysis

3.1 Atmospheric parameters

García López et al. (1995) carried out a detailed analysis of the sources of uncertainties regarding the determination of Be abundances. They concluded that the precision of the derived Be abundances is mostly dependent on the choice of the stellar atmospheric parameters. In particular, they are very sensitive to the adopted value for the surface gravity ($\log{g}$).

In order to limit the possible systematic errors in our determinations it is important, whenever possible, to use an uniform set of atmospheric parameters for all the programme stars. We thus decided to use the values listed by Santos et al. (2001a, 2001b), computed from an uniform and accurate spectroscopic analysis available for most of the stars studied in this paper. For three of the stars (HD 870, HD 1461, and HD 3823 for which no planetary companions were found to date), no parameters were available, and we computed them using CORALIE or FEROS spectra, in the very same way as in Santos et al. (2001a). The values are listed in Table 2. As discussed by the authors, the errors in $T_{\rm eff}$ are usually lower than 50 K, and errors in the microturbulence parameter are of the order of 0.1 km s^-1. As for $\log{g}$, the uncertainties are in the range of 0.10 to 0.15 dex.

 

 

Table 1: Observing log for stars with and without planets.

HD	Star	V	Observ.	S/N	Date
number			Run
Stars with planets:
HD 13445	Gl 86	6.1	UVES(A)	150	Nov. 2000
HD 16141	HD 16141	6.8	UVES(A)	120	Nov. 2000
HD 17051	$\iota$ Hor	5.4	UVES(A)	150	Nov. 2000
HD 52265	HD 52265	6.3	UVES(A)	120	Dec. 2000
HD 75289	HD 75289	6.4	UVES(A)	110	Dec. 2000
HD 82943	HD 82943	6.5	UVES(A)	140	Jan. 2001
HD 210277	HD 210277	6.5	UVES(A)	110	Nov. 2000
HD 217107	HD 217107	6.1	UVES(A)	120	Nov. 2000
-	BD-10 3166	10.0	UVES(B)	20	Feb. 2001
HD 38529	HD 38529	5.9	UVES(B)	60	Feb. 2001
HD 75289	HD 75289	6.4	UVES(B)	30	Feb. 2001
HD 92788	HD 92788	7.3	UVES(B)	40	Feb. 2001
HD 82943	HD 82943	6.5	UVES(B)	35	Feb. 2001
HD 108147	HD 108147	7.0	UVES(B)	60	Feb. 2001
HD 121504	HD 121504	7.5	UVES(B)	45	Feb. 2001
HD 134987	HD 134987	6.5	UVES(B)	60	Feb. 2001
HD 95128	47 UMa	5.1	IACUB(A)	100	May 2000
HD 114762	HD 114762	7.3	IACUB(A)	65	May 2000
HD 117176	70 Vir	5.0	IACUB(A)	70	May 2000
HD 130322	HD 130322	8.0	IACUB(A)	35	May 2000
HD 145675	14 Her	6.7	IACUB(A)	65	May 2000
HD 168443	HD 168443	6.9	IACUB(A)	55	May 2000
HD 187123	HD 187123	7.9	IACUB(A)	55	May 2000
HD 195019	HD 195019	6.9	IACUB(A)	50	May 2000
HD 10697	109 Psc	6.3	IACUB(B)	40	Oct. 2001
HD 12661	HD 12661	7.4	IACUB(B)	40	Oct. 2001
HD 22049	$\epsilon$ Eri	3.7	IACUB(B)	100	Oct. 2001
HD 9826	$\upsilon$ And	4.1	UES	120	Aug. 1998
HD 120136	$\tau$ Boo	4.5	UES	90	Aug. 1998
HD 143761	$\rho$ CrB	5.4	UES	120	Aug. 1998
HD 217014	51 Peg	5.5	UES	100	Aug. 1998
Stars without known planets:
HD 870	HD 870	7.2	UVES(A)	130	Nov. 2000
HD 1461	HD 1461	6.5	UVES(A)	120	Nov. 2000
HD 1581	HD 1581	4.2	UVES(A)	140	Dec. 2000
HD 3823	HD 3823	5.9	UVES(A)	130	Oct. 2000
HD 26965A	o2 Eri	4.4	IACUB(B)	55	Oct. 2001
HD 222335	HD 222335	7.2	UVES(A)	110	Dec. 2000

 

 

Table 2: Stellar atmospheric parameters and resulting beryllium abundances for each spectrum.

Star	$T_{\rm eff}$	$\log{g}$	[Fe/H]	$\log{N\rm (Be)}$	Run	$\log{N\rm (Li)}\dag$
Stars with planets$\dag\dag$:
BD -10 3166	6320	4.38	0.33	<0.55	UVES(B)	-
HD 9826	6140	4.12	0.12	$0.99\pm0.18$	UES	2.26
HD 10697	5605	3.96	0.16	$1.38\pm0.18$	IACUB(B)	1.94
HD 12661	5715	4.45	0.35	$1.07\pm0.14$	IACUB(B)	<0.99
HD 13445	5205	4.70	-0.20	<0.52	UVES(A)	<0.5
HD 16141	5805	4.28	0.15	$1.27\pm0.14$	UVES(A)	<0.73
HD 17051	6225	4.65	0.25	$1.02\pm0.17$	UVES(A)	2.63
HD 22049	5135	4.70	-0.07	$0.70\pm0.20$	IACUB(B)	<0.3
HD 38529	5675	4.01	0.39	<0.30	UVES(B)	<0.61
HD 52265	6100	4.29	0.24	$1.21\pm0.14$	UVES(A)	2.73
HD 75289	6135	4.43	0.27	$1.39\pm0.14$	UVES(A)	2.84
HD 75289	6135	4.43	0.27	$1.41\pm0.16$	UVES(B)	2.84
HD 75289 (avg)				1.40
HD 82943	6025	4.54	0.33	$1.32\pm0.14$	UVES(A)	2.52
HD 82943	6025	4.54	0.33	$1.22\pm0.14$	UVES(B)	2.52
HD 82943 (avg)				1.27
HD 92788	5775	4.45	0.31	$1.13\pm0.16$	UVES(B)	-
HD 95128	5800	4.25	0.01	$1.13\pm0.14$	IACUB(A)	1.71
HD 108147	6265	4.59	0.20	$1.02\pm0.14$	UVES(B)	2.34
HD 114762	5950	4.45	-0.60	$0.97\pm0.14$	IACUB(A)	2.26
HD 117176	5500	3.90	-0.03	$0.82\pm0.14$	IACUB(A)	1.76
HD 120136 $\dag\dag\dag$	6420	4.18	0.32	$0.14\pm0.30$	UES	<1.07
HD 121504	6090	4.73	0.17	$1.40\pm0.16$	UVES(B)	2.66
HD 130322	5410	4.47	0.05	$1.07\pm0.20$	IACUB(A)	<0.57
HD 134987	5715	4.33	0.32	$1.12\pm0.17$	UVES(B)	<0.69
HD 143761	5750	4.10	-0.29	$0.95\pm0.19$	UES	1.30
HD 145675	5300	4.27	0.50	<0.5	IACUB(A)	<0.7
HD 168443	5555	4.10	0.10	$0.97\pm0.15$	IACUB(A)	<0.71
HD 187123	5830	4.40	0.16	$0.98\pm0.14$	IACUB(A)	1.20
HD 195019	5830	4.34	0.09	$1.27\pm0.15$	IACUB(A)	<1.05
HD 210277	5575	4.44	0.23	$1.05\pm0.17$	UVES(A)	<0.73
HD 217014	5795	4.41	0.21	$0.98\pm0.14$	UES	1.30
HD 217107	5660	4.42	0.39	$1.01\pm0.17$	UVES(A)	<0.86
Stars from García López & Perez de Taoro (1998):
HD 75732 A	5150	4.15	0.29	<0.55	-	<0.04
HD 186408	5750	4.20	0.11	$1.10\pm0.17$	-	1.24
HD 186427	5700	4.35	0.06	$1.30\pm0.17$	-	<0.46
Stars without known planets:
HD 870	5425	4.59	-0.03	$0.84\pm0.16$	UVES(A)	<0.35
HD 1461	5785	4.47	0.18	$1.20\pm0.17$	UVES(A)	<0.71
HD 1581	5940	4.44	-0.15	$1.19\pm0.14$	UVES(A)	2.35
HD 3823	5950	4.12	-0.27	$0.98\pm0.14$	UVES(A)	2.44
HD 26965A	5185	4.73	-0.26	$0.56\pm0.20$	IACUB(B)	<0.22
HD 222335	5310	4.64	-0.10	$0.87\pm0.18$	UVES(A)	<0.35

$\dag$ The values for the Li abundances were taken from Israelian et al. (2001b); we refer to this work for references. These authors used the very same set of stellar parameters as in this paper, and thus the listed Li and Be abundances are based on the same parameter scale.
$\dag\dag$ We refer to obswww.unige.ch/~naef/who_discovered_that_planet.html for the planet discovery references.
$\dag\dag\dag$ For this star ($\tau$ Boo) the uncertainty in $\log{N({\rm Be})}$ is higher due to the "large'' $v~\sin{i}\sim15$ m s^-1.

3.2 Spectral synthesis

The abundance analysis was done in standard Local Thermodynamic Equilibrium (LTE) using a revised version of the code MOOG (Sneden 1973), and a grid of Kurucz et al. (1993) ATLAS9 atmospheres. Be abundances were derived by fitting synthetic spectra to the data, using the same line-list as in García López & Perez de Taoro (1998). While both Be II lines at 3130.420 and 3131.065 Å are present in our data, we only used the latter, given the severe line blending in the region around 3130.420 Å (used only for checking the consistency of the fit).

In the analysis, the overall metallicity was scaled to the iron abundance. We then iterated by changing the Be abundance, the continuum placement and the Gaussian smoothing profile until the best fit for the whole spectral region was obtained (we fitted all the spectrum between 3129.5 and 3132.0 Å). When considered important (e.g. for $\tau$ Boo), the smoothing function used was a combination of a Gaussian and a rotational profile; for these cases we used the $v~\sin{i}$ value determined from the width of the CORAVEL cross-correlation dip (Benz & Mayor 1984). Three examples are shown in Figs. 1 and 2. The resulting abundances for all the objects observed are listed in Table 2. Here we use the notation $\log{N\rm (Be)}=[\rm Be]=\log{{\rm (Be/H})}+12$.

3.3 Errors

It is not simple to derive accurate uncertainties for measurements of Be abundances (García López et al. 1995). In this paper the errors were estimated as follows. We considered that from the errors of $\pm$50 K in temperature and $\pm$0.15 dex in $\log{g}$ we can expect typical uncertainties around 0.03 and 0.06 dex, respectively. There are several OH lines blended with the Be II 3130.420 Å line; changes in the oxygen abundance would also change the location of the pseudo-continuum in that region, affecting the overall fit. To take this into account, an error of 0.05 dex, associated with the uncertainties in the oxygen abundances expected for these stars, has been added. Other atmospheric parameters, like the metallicity [Fe/H] and the microturbulence, do not influence significantly the results, and we will conservatively consider that together they introduce an error of 0.05. Adding quadratically, these figures produce an uncertainty of 0.09 dex, that was added to the error due to continuum placement and fit quality for each case, that we conservatively considered to be at least of 0.10 dex. The final errors, listed in Table 2 together with the derived Be abundances, are of the order of 0.16 dex, and quite independent of the S/N of the spectrum.

Note that we are interested in carrying out a differential analysis, and thus the knowledge of the absolute temperatures and surface gravities is not very important. Rather, it is crucial that these values are all in the same "scale''.