By cross-correlating the results of two recent large-scale surveys, the general properties of a well defined sample of semi-regular variable stars have been determined. ISOGAL mid-infrared photometry (7 and 15 µm) and MACHO V and R lightcurves are assembled for approximately 300 stars in the Baade's Windows of low extinction towards the Galactic bulge. These stars are mainly giants of late M spectral type, evolving along the asymptotic giant branch (AGB). They are found to possess a wide and continuous distribution of pulsation periods and to obey an approximate log period -bolometric magnitude (log P -M bol ) relation or set of such relations.Approximate mass-loss ratesṀ in the range of ∼1 × 10 −8 to 5 × 10 −7 M ⊙ year −1 are derived from ISOGAL mid-infrared photometry and models of stellar spectra adjusted for the presence of optically-thin circumstellar silicate dust. Mass-loss rates depend on luminosity and pulsation period. Some stars lose mass as rapidly as short-period Miras but do not show Mira-like amplitudes. A period of 70 days or longer is a necessary but not a sufficient condition for mass loss to occur.For AGB stars in the mass-loss ranges that we observe, the functional dependence of mass-loss rate on temperature and luminosity can be expressed asṀ ∝ T α L β , where α = −8.80 +0.96 −0.24 and β = +1.74 +0.16 −0.24 , in agreement with recent theoretical predictions. If we include our mass-loss rates with a sample of extreme mass-losing AGB stars in the Large Magellanic Cloud, and ignore T as a variable, we get the general result for AGB stars thatṀ ∝ L 2.7 , valid for AGB stars with 10 −8 <Ṁ < 10 −4 M ⊙ yr −1 .

Abstract. We present a study of known OH/IR stars in the inner bulge, observed by the ISOGAL survey at λ = 6.8 µm and λ = 14.9 µm. Bolometric corrections and luminosities are computed, based on near and mid-infrared data. The vast majority of the sources exhibit mass-loss rates in the range: 3 × 10 −7 up to a few times 10 −5 M /year. The bolometric magnitude distribution peaks at M bol = −5.0. There is no clear evidence that the luminosity is related to the expansion velocity of the envelope for the sample in the bulge observed by ISOGAL. We find that the bulge OH/IR stars do not follow a period-luminosity (PL) law and that they are systematically less luminous than the OH/IR extension of the PL relationship for Miras.

A B S T R A C TThe ISOGAL mid-infrared survey of areas close to the Galactic plane aims to determine the stellar content of those areas, and its possible bearing on the history of the Galaxy. The NGC 6522 and Sgr I Baade's Windows of low obscuration towards the inner parts of the Galactic bulge represent ideal places in which to calibrate and understand the ISOGAL colour± magnitude diagrams, which are more difficult to interpret in heavily reddened fields.The survey observations were made with the ISOCAM instrument of the ISO satellite. The filter bands chosen were LW2 (, 7 mm) and LW3 (, 15 mm).The results presented here show that most of the detected objects are late M-type giants on the asymptotic giant branch (AGB), with a cut-off for those earlier than M3±M4. The most luminous members of these two bulge fields at 7 mm are the Mira variables. However, it is evident that they represent the end of a sequence of increasing 15-mm dust emission which commences with M giants of an earlier sub-type.In observations of late-type M giants, the ISOCAM 15-mm band is mainly sensitive to the cool silicate or aluminate dust shells which overwhelm the photospheric emission. However, in ordinary M-giant stars, the 7-mm band is not strongly affected by dust emission and may be influenced instead by absorption. The n 2 band of water at 6.25 mm and the SiO fundamental at 7.9 mm are likely contributors to this effect. Miras are more luminous at 7 mm and have redder K 0 ±[7] colours than other M giants. Their [7]±[15] colours are consequently bluer than might be expected by extrapolating from warmer M giants.A group of late-M stars has been found that vary little or not at all, but have infrared colours typical of well-developed dust shells. Their luminosities are similar to those of 200±300 day Miras, but they have slightly redder [7]±[15] colours which form an extension of the ordinary M-giant sequence. They may belong to the class of red semi-regular variables.The Mira dust shells show a mid-infrared [7]±[15] colour±period relation. In these two fields there is no component of high-luminosity late-type variables obscured at K and shorter wavelengths such as is seen in the Magellanic Clouds. The upper limit of long-period variable (LPV) periods in these fields remains at approximately 700 d.