2 Sample and observations

This section describes the two-year-long monitoring of a large sample of LPV stars performed with ELODIE at the Observatoire de Haute-Provence (France) at a frequency of about one night per month, weather-permitting.

   
2.1 The spectrovelocimeter ELODIE

The fibre-fed echelle spectrograph ELODIE (Baranne et al. 1996) is mounted on the 1.93-m telescope of the Observatoire de Haute-Provence (France). This instrument is designed to perform very accurate radial-velocity measurements by cross-correlating the stellar spectrum with numerical masks. In one exposure an echelle spectrum at a resolution of 42000 ranging from 3906 Å to 6811 Å is recorded. Then, an automatic on-line data processing extracts a 2-D spectrum (67 orders $\times$ 1044 pixels) from the echelle spectrum. We developed our own cross-correlation procedure, following the prescriptions of Baranne et al. (1996). We have thus the possibility of using our own numerical templates and to perform different kinds of tests in the computation of the cross-correlation function (CCF). The CCF is computed directly from the 2-D spectrum. First, it is wavelength-calibrated, then corrected from the value of the Earth barycentric velocity towards the star. To preserve the accuracy, the CCF is computed without either rebinning or merging the orders. Only orders having an average signal-to-noise (S/N) ratio greater than 2.0 are used.

Two templates have been systematically used in a first step to compute the CCFs of the whole sample: (i) the default K0III mask provided in the ELODIE reduction software (Baranne et al. 1996); (ii) a M4V mask constructed by Delfosse et al. (1999) from an ELODIE spectrum of Barnard's star (Gl 699) applying the method of Baranne et al. (1979). Although the K0III template may in fact seem inadequate to study much cooler LPVs, it was argued in Sect. 2.2 of Alvarez et al. (2001; hereafter Paper II) that "warm'' masks like the K0III one are more prone to detect line doubling (see also Sects. 3 and 4.3.2.1). On the other hand, it has been checked a posteriori (see the discussion in Sect. 4.3.2.1 in relation with Fig. 10) that the M4V mask yields CCFs that are identical to those obtained with a mask mimicking the spectrum of the M4.5III star HD 123657 (see Table 1).

2.2 The sample

The sample is composed of: (i) 6 circumpolar Miras (SUCam, SUMi, RTDra, AXCep, SCep, RYCep) that can be observed all along the pulsational cycle; (ii) 76 LPVs (Mira and semi-regular variables) of different periods, chemical compositions, spectral types and brightness ranges, observed at different phases; (iii) 8 non-LPV red giants; (iv) 3 radial-velocity standard stars. The entire sample (93 stars) is presented in Table 1: for each star are indicated its GCVS (General Catalogue of Variable Stars, Kholopov et al. 1988) name (or the HD number); its right ascension and declination (2000.0); its variability type, period, spectral type and brightness range as given by the GCVS; the number of observations N. The last column indicates whether the star is circumpolar ("circum.''), non-LPV ("non-LPV'') or radial-velocity standard ("r.v. st.'').

 

 

Table 1: Sample stars.

Name	Right Asc.	Declination	Variability	Period	Spectral	Brightness	N	Comments
	(2000.0)	(2000.0)	Type	(d)	Type	Range
SV And	00:04:20	+40:06:36	Mira	316.21	M5e-M7e	7.7-14.3	2
T And	00:22:23	+26:59:46	Mira	280.76	M4e-M7.5e	7.7-14.5	2
R And	00:24:02	+38:34:39	Mira	409.33	S3,5e-S8,8e	5.8-14.9	1
Y Cep	00:38:22	+80:21:24	Mira	332.57	M5e-M8.2e	8.1-16.0	1
U Psc	01:22:58	+12:41:54	Mira	173.10	M4e	10.3-14.9	1
R Psc	01:30:38	+02:52:55	Mira	344.50	M3e-M6e	7.0-14.8	5
Y And	01:39:37	+39:20:37	Mira	220.53	M3e-M4.5e	8.2-15.1	5
o Cet	02:19:21	-02:58:28	Mira	331.96	M5e-M9e	2.0-10.1	3
R Cet	02:26:02	-00:10:42	Mira	166.24	M4e-M9	7.2-14.0	7
U Cet	02:33:44	-13:08:54	Mira	234.76	M2e-M6e	6.8-13.4	1
R Tri	02:37:02	+34:15:54	Mira	266.9	M4IIIe-M8e	5.4-12.6	3
U Ari	03:11:03	+14:47:58	Mira	371.13	M4e-M9.5e	7.2-15.2	5
SS Cep	03:49:30	+80:19:20	SRb	90.0	M5III	8.0- 9.1	3
R Tau	04:28:18	+10:09:44	Mira	320.90	M5e-M9e	7.6-15.8	4
V Tau	04:52:02	+17:32:18	Mira	168.7	M0e-M4.5e	8.5-14.6	4
R Aur	05:17:18	+53:35:11	Mira	457.51	M6.5e-M9.5e	6.7-13.9	3
W Aur	05:26:55	+36:54:11	Mira	274.27	M3e-M8e	8.0-15.3	2
RU Aur	05:40:08	+37:38:12	Mira	466.47	M7e-M9e	9.0-16.0	3
S Cam	05:41:02	+68:47:55	SRa	327.26	C7,3e(R8e)	7.7-11.6	5
$\alpha$ Ori	05:55:10	+07:24:25	SRc		M1	0.50	1	non-LPV
U Ori	05:55:49	+20:10:31	Mira	368.3	M6e-M9.5e	4.8-13.0	4
$\delta$ Aur	05:59:31	+54:17:11			K0	3.71	1	non-LPV
X Aur	06:12:13	+50:13:41	Mira	162.79	M3e-M7e	8.0-13.6	2
$\mu$ Gem	06:22:57	+22:30:54	Lb		M3	2.97	1	non-LPV
SU Cam	06:38:12	+73:55:00	Mira	285.03	M5	8.9-12.6	8	circum.
X Gem	06:47:07	+30:16:35	Mira	264.16	M5e-M8e(Tc:)	7.5-13.8	3
X Mon	06:57:12	-09:03:51	SRa	155.80	M1eIII-M6ep	6.8-10.2	1
R Gem	07:07:21	+22:42:13	Mira	369.91	S2.9e-S8.9e	6.0-14.0	7
R CMi	07:08:43	+10:01:27	Mira	337.78	C7,1Je(CSep)	7.25-11.6	1
S CMi	07:32:43	+08:19:07	Mira	332.94	M6e-M8e	6.6-13.2	5
$\upsilon$ Gem	07:35:55	+26:53:50			M0	4.06	1	non-LPV
81 Gem	07:46:08	+18:30:39			K4	4.87	1	non-LPV
R Cnc	08:16:34	+11:43:35	Mira	361.6	M6e-M9e	6.07-11.8	5
X UMa	08:40:49	+50:08:11	Mira	249.04	M3e-M4e	8.1-14.8	4
HD 76830	08:59:11	+18:08:09			M4	6.38	1	non-LPV
UZ Hya	09:16:45	-04:36:24	Mira	260.95	M4e	8.8-14.5	5
R Leo	09:47:33	+11:25:46	Mira	309.95	M6e-M8IIIe	4.4-11.3	3
S LMi	09:53:43	+34:55:32	Mira	233.83	M2.0e-M8.2e	7.5-14.3	2
V Leo	10:00:02	+21:15:40	Mira	273.35	M5e	8.4-14.6	4
R UMa	10:44:39	+68:46:33	Mira	301.62	M3e-M9e	6.5-13.7	4
RU UMa	11:41:40	+38:28:30	Mira	252.46	M3e-M5e	8.1-15.0	4
Y Vir	12:33:52	-04:25:18	Mira	218.43	M2e-M5e	8.3-15.0	4
R Vir	12:38:30	+06:59:18	Mira	145.63	M3.5IIIe-M8	6.1-12.1	2
RS UMa	12:38:57	+58:29:03	Mira	258.97	M4e-M6e	8.3-14.9	4
S UMa	12:43:57	+61:05:36	Mira	225.87	S0,9e-S5,9e	7.1-12.7	2
U Vir	12:51:06	+05:33:12	Mira	206.64	M2e-M8e:	7.4-13.5	2
V UMi	13:38:41	+74:18:37	SRb	72.0	M5IIIab	7.2- 9.1	5
SY Vir	13:58:38	-04:34:35	Mira	236.65	M6:	9.6-13.4	1
HD 123657	14:07:56	+43:51:18	Lb		M4.5III	5.25	1	non-LPV
$\alpha$ Boo	14:15:38	+19:11:06			K1.5III	-0.04	1	r.v. st
R Boo	14:37:12	+26:44:12	Mira	223.4	M3e-M8e	6.2-13.1	5
Y Lib	15:11:41	-06:00:43	Mira	275.70	M5e-M8.2e	7.6-14.7	4
RT Boo	15:17:15	+36:21:34	Mira	273.86	M6.5e-M8e	8.3-13.9	2
S Ser	15:21:40	+14:18:52	Mira	371.84	M5e-M6e	7.0-14.1	1
S UMi	15:29:35	+78:38:00	Mira	331.0	M6e-M9e	7.5-13.2	10	circum.
ST Her	15:50:47	+48:29:00	SRb	148.0	M6	8.8-10.3	1
RU Her	16:10:15	+25:04:14	Mira	484.83	M6e-M9	6.8-14.3	7
SS Oph	16:57:52	-02:45:42	Mira	180.64	M5e	7.8-14.5	1
RV Her	17:00:35	+31:13:22	Mira	205.23	M2e	9.0-15.5	1
SY Her	17:01:29	+22:28:40	Mira	116.91	M1e-M6e	8.4-14.0	1
Z Oph	17:19:32	+01:30:52	Mira	348.7	K3ep-M7.5	7.6-14.0	10
RS Her	17:21:42	+22:55:16	Mira	219.70	M4e-M8	7.0-13.0	3
RU Oph	17:32:53	+09:25:24	Mira	202.29	M3e-M5e	8.6-14.2	1
$\beta$ Oph	17:43:27	+04:34:03			K2III	2.77	6	r.v. st
T Her	18:09:06	+31:01:16	Mira	164.98	M2,5e-M8e	6.8-13.7	1
RY Oph	18:16:37	+03:41:34	Mira	150.41	M3e-M6	7.4-13.8	1
RT Dra	18:19:26	+72:40:50	Mira	279.41	M5	9.6-13.8	14	circum.
SV Her	18:26:23	+25:01:35	Mira	238.99	M5e	9.1-15.1	1
X Oph	18:38:21	+08:50:01	Mira	328.85	M5e-M9e	5.9- 9.2	4
WZ Lyr	19:02:15	+47:12:56	Mira	376.64	M9e	10.6-15.0	2
RU Lyr	19:12:21	+41:18:12	Mira	371.84	M6e:-M8e	9.5-15.9	1
W Aql	19:15:23	-07:02:50	Mira	490.43	S3,9e-S6,9e	7.3-14.3	1
RT Cyg	19:43:38	+48:46:41	Mira	190.28	M2e-M8.8eIb	6.0-13.1	7
$\gamma$ Aql	19:46:14	+10:36:43			K3II	2.72	3	r.v. st
$\chi$ Cyg	19:50:34	+32:54:53	Mira	408.05	S6,2e-S10,4e	3.3-14.2	6

 

 

Table 1: continued.

Name	Right Asc.	Declination	Variability	Period	Spectral	Brightness	N	Comments
	(2000.0)	(2000.0)	Type	(d)	Type	Range
Z Cyg	20:01:27	+50:02:34	Mira	263.69	M5e-M9e	7.1-14.7	1
S Aql	20:11:37	+15:37:13	SRa	146.45	M3e-M5.5e	8.9-12.8	1
Z Aql	20:15:11	-06:09:04	Mira	129.22	M3e	8.2-14.8	1
WX Cyg	20:18:34	+37:26:54	Mira	410.45	C8,2JLi(N3e)	8.8-13.2	2
T Cep	21:09:32	+68:29:28	Mira	388.14	M5.5e-M8.8e	5.2-11.3	6
RR Aqr	21:15:01	-02:53:43	Mira	182.45	M2e-M4e	9.1-14.4	1
X Peg	21:21:00	+14:27:00	Mira	201.20	M2e-M5e	8.8-14.4	1
SW Peg	21:22:29	+21:59:45	Mira	396.33	M4e	8.0-14.0	2
AX Cep	21:26:52	+70:13:18	Mira	395.0	C(N)	9.5-13.0	11	circum.
S Cep	21:35:13	+78:37:28	Mira	486.84	C7,4e(N8e)	7.4-12.9	12	circum.
RV Peg	22:25:38	+30:28:22	Mira	396.80	M6e	9.0-15.5	1
AR Cep	22:51:33	+85:02:47	SRb		M4III	7.0-7.9	2	non-LPV
R Peg	23:06:39	+10:32:35	Mira	378.1	M6e-M9e	6.9-13.8	4
W Peg	23:19:50	+26:16:44	Mira	345.5	M6e-M8e	7.6-13.0	5
S Peg	23:20:33	+08:55:08	Mira	319.22	M5e-M8.5e	6.9-13.8	3
RY Cep	23:21:14	+78:57:31	Mira	149.06	Ke-M0e	8.6-13.6	9	circum.
ST And	23:38:45	+35:46:17	SRa	328.34	C4,3e-C6,4e	7.7-11.8	5
R Cas	23:58:24	+51:23:18	Mira	430.46	M6e-M10e	4.7-13.5	4

2.3 The observations

A total of 27 observing nights on ELODIE were allocated between 1998, August and 2000, August (more or less one night per month). Approximatively one third of the total observing time was lost mainly because of bad atmospheric conditions, causing interruptions in the phase coverage. About 15-20 stars were observed during each clear night, with typical exposure times of about 25 min yielding a S/N ratio per resolution element at 500 nm up to 150 for the brightest stars. For the faintest and reddest stars, sometimes only the reddest orders recorded a usable signal. But the power of a correlation technique is precisely that it does not require high S/N spectra to deliver useful CCFs (see e.g., Queloz 1995). As indicated in Sect. 2.1, the CCF is computed using orders having an average S/Nratio of at least 2.0.

The log of observations is presented in Table 2: the first and second columns list the civil date and the corresponding Julian date at midnight. The third column gives the code number of the night: each observing night will be subsequently referred to by this number. Only the nights during which at least one star was observed are reported in Table 2.

A total of 315 spectra were collected, i.e. 3-4 spectra per star on average. Some (circumpolar) stars were observed as often as 12 times (SCep), and the majority of variable stars were observed 2-3 times.