Previous studies have shown that mass loss rates increase with increasing pulsation periods in Miras. For example, Whitelock (1990) and Whitelock et al. (1994) derived the mass loss rates for oxygen-rich Miras in the Galactic Bulge and the South Galactic Cap, respectively, and found this trend. The mass loss rates were based on dust emission and then converted to a total mass loss rate based on a constant dust-to-gas ratio and expansion velocity for all stars in their respective samples.

In a different approach to derive the dust mass loss rate, Groenewegen et al. (1998) fitted the Spectral Energy Distributions (SEDs) and mid-infrared IRAS LRS spectra of 44 carbon Mira variables with a dust radiative transfer model. In that paper the total mass loss rate was then derived from a modified relation between the photon momentum transfer rate (L/c) and the momentum transfer rate of the wind ( $\dot{M}$ $v_{\infty}$ ).

There is an alternative method to derive the total mass loss rate and that is through molecular emission lines, notably CO which is the most abundant molecule after H₂. Many CO observations have been published for AGB stars over the past years (see Loup et al. 1993 for a compilation up to that epoch; more recent work include Bieging & Latter 1994; Sahai & Liechti 1995; Young 1995; Groenewegen et al. 1996; Knapp et al. 1998; Olofsson et al. 1998; Neri et al. 1998; Kerschbaum & Olofsson 1998; Groenewegen & de Jong 1998). CO observations are the main focus here as well. As the results in Groenewegen et al. (1998) suggested that the overall good relation between mass loss rate and pulsation period might break down for periods shorter than about 400 days we concentrated on the shorter period range, and also included both O- and C-rich Miras. This possible breakdown of a mass loss-period relation might be related to the fact that radiation pressure on dust is no longer sufficient to drive the mass loss at lower luminosity (Dominik et al. 1990).

The paper is organised as follows. In Sect. 2 the sample of stars is introduced and the millimeter observations are described. In Sect. 3 the line profiles and observational results are presented. In Sect. 4 the infrared observations are described. In Sect. 5 the analysis is performed, which includes the modelling of the SEDs and LRS spectra for 7 stars, estimation of luminosity and distance using several methods, derivation of the dust- and gas-mass loss rate. In Sect. 6 we comment on the various correlations between mass loss rate and pulsation period, expansion velocity, etc.

**Table 1:** The sample
Name	R.A.	Dec.	Type	Period	References
	(1950)	(1950)		(days)

IRAM December 1994 run
V390 Cas	01 25 16.3	+62 01 09	C	362^a
PT Cas	01 34 51.5	+55 42 56	C	300
CN Per	02 03 12.7	+56 36 43	C	384
R For	02 27 01.31	-26 19 14.8	C	388.7	Loup et al. (1993), Olofsson et al. (1993, 1998)
AFGL 5076	02 34 34.6	+54 22 19	C	-	Volk et al. (1993)
IRAS 02408+5458	02 40 49.1	+54 58 35	C	-
GY Per	04 25 50.76	+39 27 11.2	C	377.8
UV Aur	05 18 33.31	+32 27 51.4	C	394.2^b	SIMBAD
ZZ Gem	06 20 56.5	+25 03 31	C	317.0
AFGL 935	06 23 04.64	-09 30 20.1	C	494	Loup et al. (1993)
IRAS 06582+1507	06 58 17.3	+15 07 58	C	-	Loup et al. (1993), Volk et al. (1993)
R CMi	07 05 57.56	+10 06 16.1	C	337.8	SIMBAD
VX Gem	07 09 58.6	+14 41 11	C	379.4	SIMBAD
C1698	07 22 09.3	-04 31 58	C	-	Engels (1994)
R Pyx	08 43 23.8	-28 01 04	C	364.7
V CrB	15 47 43.89	+39 43 20.5	C	357.6	Loup et al. (1993), Olofsson et al. (1993),
					Knapp et al. (1998), Neri et al. (1998)
V Oph	16 23 56.58	-12 18 54.7	C	297.2
AFGL 2310	19 00 53.05	+07 26 21.9	C	577	Loup et al. (1993), Likkel & Miao (1996)
AFGL 2368	19 17 35.39	-08 07 51.0	C	676	Loup et al. (1993)
AFGL 2686	20 57 00.28	+27 14 51.4	C	750	Loup et al. (1993)
V1549 Cyg	21 03 32.6	+51 36 18	C	533	Loup et al. (1993)
AX Cep	21 26 15.0	+70 00 16	C	395.0
AFGL 5625	21 31 50.1	+56 31 13	C	-	Loup et al. (1993), Volk et al. (1993), Neri et al. (1998)
CIT 13	21 32 06.06	+38 50 52.9	C	470	Loup et al. (1993), Olofsson et al. (1993)
AO Lac	22 40 35.9	+51 15 36	C	300
LS Cas	23 35 45.8	+55 45 12	C	340
AFGL 230	01 30 27.63	+62 11 31.2	O	1525	Loup et al. (1993), Neri et al. (1998)
AFGL 5093	03 20 41.48	+65 21 32.8	O	1276	Loup et al. (1993)
AFGL 5097	03 29 23.65	+60 10 04.4	O	-	Loup et al. (1993)
NV Aur	05 07 19.68	+52 48 53.9	O	635	Loup et al. (1993)
AFGL 712	05 13 06.6	+45 30 48	O	1088
IRAS 05284+1945	05 28 27.2	+19 45 08	O	-
IRAS 06403-0138	06 40 19.1	-01 38 05	O	-
IRAS 07113-2747	07 11 23.1	-27 47 46	O	-
OH 10.1-0.1	18 05 17.95	-20 16 41.0	O	-	Blommaert et al. (1994)
IRAS 21554+6204	21 55 29.6	+62 04 24	O	-	Loup et al. (1993)
AFGL 2885	22 17 42.7	+59 36 17	O	1570	Loup et al. (1993)
AFGL 2968	22 48 00.9	+60 02 01	O	-	Josselin et al. (1998)

IRAM January 1995 run
Y Per	03 24 18.07	+44 00 12.6	C	248.6
R Ori	04 56 17.62	+08 03 19.7	C	377.1
V Aur	06 20 15.4	+47 44 03	C	353.0
ZZ Gem	06 20 56.5	+25 03 31	C	317.0
R CMi	07 05 57.56	+10 06 16.1	C	337.8
R Pyx	08 43 23.8	-28 01 04	C	364.7
V CrB	15 47 43.89	+39 43 20.5	C	357.6	see above
V Oph	16 23 56.58	-12 18 54.7	C	297.2
AX Cep	21 26 15.0	+70 00 16	C	395.0
U Ori	05 52 50.95	+20 10 08.1	O	368.3	Young (1995), Knapp et al. (1998)
R LMi	09 42 34.75	+34 44 33.9	O	372.2	Loup et al. (1993), Young (1995)
R Leo	09 44 52.22	+11 39 42.0	O	310.0	Loup et al. (1993), Bieging & Latter (1994),
					Young (1995), Stanek et al. (1995), Olofsson et al. (1998)
RS Vir	14 24 46.00	+04 54 06.3	O	354.0
R Ser	15 48 23.26	+15 17 03.1	O	356.4	Loup et al. (1993), Young (1995), Knapp et al. (1998)
X Oph	18 35 57.57	+08 47 19.9	O	328.9	Young (1995)
R Peg	23 04 08.27	+10 16 22.8	O	378.1	Young (1995)

IRAM August 1995 run
R Cet	02 23 28.71	-00 24 11.0	O	166.2
R Tri	02 34 00.02	+34 02 51.6	O	266.9	SIMBAD
R Tau	04 25 33.46	+10 03 08.9	O	320.9
T Lep	05 02 43.20	-21 58 18.7	O	368.1
X Hya	09 33 06.94	-14 28 03.5	O	301.1	Young (1995)
R Aqr	23 41 14.18	-15 33 41.8	O	387.0

JCMT August 1995 run
R For	02 27 01.31	-26 19 14.8	C	388.7	see above
UV Aur	05 18 33.31	+32 27 51.4	C	394.2	see above

**Table 1:** continued
Name	R.A.	Dec.	Type	Period	References
	(1950)	(1950)		(days)

R Cap	20 08 30.18	-14 25 02.3	C	345.1
AX Cep	21 26 15.0	+70 00 16	C	395.0
S Scl	00 12 51.11	-32 19 22.5	O	362.7	Cho et al. (1996), Haikala (1990)
R Cet	02 23 28.71	-00 24 11.0	O	166.2
RT Eri	03 31 54.33	-16 19 51.1	O	370.8
W Eri	04 09 25.24	-25 15 43.3	O	376.6
RS Eri	04 15 41.82	-18 37 42.8	O	296.0	Lewis (1997)
R Tau	04 25 33.46	+10 03 08.9	O	320.9
BD Eri	04 31 11.28	-00 04 37.6	O	336	Benson & Little-Marenin (1996)
T Lep	05 02 43.20	-21 58 18.7	O	368.1
U Ori	05 52 50.95	+20 10 08.1	O	368.3	see above
X Oph	18 35 57.57	+08 47 19.9	O	328.9	see above
RT Aql	19 35 40.42	+11 36 27.6	O	327.1	Young (1995)
BG Cyg	19 36 56.87	+28 23 51.4	O	419.8^c
Z Cyg	20 00 02.6	+49 54 07	O	263.7	Young (1995), Josselin et al. (1998)
RU Cap	20 29 39.36	-21 51 39.6	O	347.4
TU Peg	21 42 39.21	+12 28 05.1	O	321.6
R Peg	23 04 08.27	+10 16 22.8	O	378.1	see above
W Peg	23 17 22.65	+26 00 18.4	O	345.5	Young (1995)
R Aqr	23 41 14.18	-15 33 41.8	O	387.0

SEST September 1996 run
AFGL 971	06 34 16.4	+03 28 05	C	653	Loup et al. (1993), Knapp et al. (1998)
CL Mon	06 52 55.9	+06 26 37	C	497.2	Loup et al. (1993), Olofsson et al. (1993), Neri et al. (1998)
R CMi	07 05 57.56	+10 06 16.1	C	337.8
R Vol	07 06 32.6	-72 56 01	C	453.6	Loup et al. (1993), Olofsson et al. (1993, 1998)
R Pyx	08 43 23.8	-28 01 04	C	364.7
V Cru	12 53 36.64	-57 37 44.1	C	376.5
R Cap	20 08 30.18	-14 25 02.3	C	345.1
RZ Peg	22 03 39.05	+33 15 39.7	C	438.7	SIMBAD
o Cet	02 16 49.05	-03 12 13.4	O	332.0	Loup et al. (1993), Young (1995), Bujarrabal et al. (1994),
					Stanek et al. (1995), Knapp et al. (1998)
U Ari	03 08 16.56	+14 36 41.9	O	371.1	Young (1995)
RT Eri	03 31 54.33	-16 19 51.1	O	370.8
U Hor	03 51 11.83	-45 58 40.3	O	348.4	Haikala et al. (1994)
W Eri	04 09 25.24	-25 15 43.3	O	376.6
R Tau	04 25 33.46	+10 03 08.9	O	320.9
RX Tau	04 35 31.75	+08 14 13.9	O	331.8	Duflot et al. (1995)
R Cae	04 38 45.87	-38 19 51.3	O	391.0	Haikala et al. (1994)
T Lep	05 02 43.20	-21 58 18.7	O	368.1
U Dor	05 09 50.90	-64 22 42.6	O	394.4	Loup et al. (1993)
RT Lep	05 40 28.76	-23 43 02.7	O	399.0
U Ori	05 52 50.95	+20 10 08.1	O	368.3	see above
AS Pup	08 07 50.32	-38 01 34.7	O	324.7	Haikala et al. (1994)
R Car	09 30 59.21	-62 34 01.1	O	308.7
W Vel	10 13 22.67	-54 13 44.8	O	394.7
RZ Mus	12 57 30.64	-70 41 35.3	O	333.7
AQ Cen	14 02 01.96	-35 15 31.8	O	387.5
RU Hya	14 08 40.87	-28 39 01.0	O	331.5
Y Lup	14 55 56.79	-54 46 02.7	O	396.8
S Ser	15 19 18.97	+14 29 35.0	O	371.8
RS Lib	15 21 24.28	-22 44 05.4	O	217.7	Young (1995)
BG Ser	15 41 01.46	-01 33 11.7	O	143^d
R Ser	15 48 23.26	+15 17 03.1	O	356.4	see above
RR Sco	16 53 26.31	-30 30 08.3	O	281.5	Young (1995)
RW Sco	17 11 34.82	-33 22 32.5	O	388.5
V545 Oph	17 36 43.78	-23 19 49.4	O	223
V438 Sco	17 53 51.45	-37 28 41.3	O	392.0
WY Her	17 57 59.53	+23 35 41.3	O	376
X Oph	18 35 57.57	+08 47 19.9	O	328.9	see above
V342 Sgr	19 09 21.19	-32 56 05.4	O	372	Loup et al. (1993)
W Aql	19 12 41.6	-07 08 08	O	490.4	Loup et al. (1993), Bieging & Latter (1994), Sahai & Liechti (1994),
					Bieging et al. (1999), Knapp et al. (1998)
RT Aql	19 35 40.42	+11 36 27.6	O	327.1	see above
RR Sgr	19 52 49.89	-29 19 23.6	O	336.3
RR Aql	19 55 00.41	-02 01 17.5	O	394.8	Loup et al. (1993), Olofsson et al. (1998)

**Table 1:** continued
Name	R.A.	Dec.	Type	Period	References
	(1950)	(1950)		(days)

SEST September 1997 run
RZ Peg	22 03 39.05	+33 15 39.7	C	438.7
o Cet	02 16 49.05	-03 12 13.4	O	332.0	see above
RT Eri	03 31 54.33	-16 19 51.1	O	370.8
AQ Cen	14 02 01.96	-35 15 31.8	O	387.5
Y Lup	14 55 56.79	-54 46 02.7	O	396.8
RR Sco	16 53 26.31	-30 30 08.3	O	281.5	see above
RW Sco	17 11 34.82	-33 22 32.5	O	388.5
V438 Sco	17 53 51.45	-37 28 41.3	O	392.0
V342 Sgr	19 09 21.19	-32 56 05.4	O	372	see above
RR Sgr	19 52 49.89	-29 19 23.6	O	336.3
RR Aql	19 55 00.41	-02 01 17.5	O	394.8	see above

SEST September 1998 run
AFGL 971	06 34 16.4	+03 28 05	C	653.	see above
R Vol	07 06 32.6	-72 56 01	C	453.6	see above
R Cap	20 08 30.18	-14 25 02.3	C	345.1
U Ari	03 08 16.56	+14 36 41.9	O	371.1	see above
W Eri	04 09 25.24	-25 15 43.3	O	376.6
R Tau	04 25 33.46	+10 03 08.9	O	320.9
RX Tau	04 35 31.75	+08 14 13.9	O	331.8
T Lep	05 02 43.20	-21 58 18.7	O	368.1
U Dor	05 09 50.90	-64 22 42.6	O	394.4
U Ori	05 52 50.95	+20 10 08.1	O	368.3	see above
R Car	09 30 59.21	-62 34 01.1	O	308.7
W Vel	10 13 22.67	-54 13 44.8	O	394.7
RZ Mus	12 57 30.64	-70 41 35.3	O	333.7
AQ Cen	14 02 01.96	-35 15 31.8	O	387.5
Y Lup	14 55 56.79	-54 46 02.7	O	396.8
V545 Oph	17 36 43.78	-23 19 49.4	O	223
X Oph	18 35 57.57	+08 47 19.9	O	328.9	see above

Notes. (a) Currently (Nov. 1998) listed in SIMBAD as a possibly Semi-Regular (SR) without period. (b) Currently listed in SIMBAD as a SR with a period of 393.4 days. (c) Currently listed in SIMBAD with a period of 291 days! The HIPPARCOS output catalog (ESA 1997) lists a period of 287.3 days. (d) The HIPPARCOS output catalog lists a period of 404 days.

Comparing the SIMBAD database with the periods listed in the 4th edition of the GCVS shows that there are four stars for which the periods changed by more than 4 days: AX Cep (399.1), U Ori (372.5), X Oph (334.2) and Y Lup (402.1).

Some stars have been assigned variable star names (as of Nov. 1998): AFGL 230 (V669 Cas), AFGL 935 (V713 Mon), AFGL 971 (V688 Mon), AFGL 2310 (V1418 Aql), AFGL 2368 (V1420 Aql), CIT 13 (V1426 Cyg).

1 Introduction