M. Ferrari-Toniolo

Mid-Infrared Photometry of Mass-losing Asymptotic Giant Branch Stars

We present ground-based mid-IR imaging for 27 M-, S-, and C-type asymptotic giant branch (AGB) stars. The data are compared with those of the database available thanks to the IRAS, Infrared Space Observatory, Midcourse Space Experiment, and Two Micron All Sky Survey catalogs. Our goal is to establish relations between the IR colors, the effective temperature Teff, the luminosity L, and the mass-loss rate , for improving the effectiveness of AGB modeling. Bolometric (absolute) magnitudes are obtained through distance compilations and by applying previously derived bolometric corrections; the variability is also studied, using data accumulated since the IRAS epoch. The main results are as follows: (1) Values of L and for C stars fit relations previously established by us, with Mira variables being on average more evolved and mass-losing than semiregular variables. (2) Moderate IR excesses (as compared to evolutionary tracks) are found for S and M stars in our sample: they are confirmed to originate from the dusty circumstellar environment. (3) A larger reddening characterizes C-rich Mira variables and post-AGB stars. In this case, part of the excess is due to AGB models overestimating Teff for C stars, as a consequence of the lack of suitable molecular opacities. This has a large effect on the colors of C-rich sources, and sometimes disentangling the photospheric and circumstellar contributions is difficult; better model atmospheres should be used in stellar evolutionary codes for C stars. (4) The presence of a long-term variability at mid-IR wavelengths seems to be limited to sources with maximum emission in the 8-20 μm region, usually Mira variables (one-third of our sample). Most of the semiregular and post-AGB stars studied here have remained remarkably constant in the mid-IR over the last 20 years.

A search for young stellar objects in southern dark clouds

The IRAS Point Source Catalog has been used to search 482 southern dark clouds for evidence of young stellar objects. Only 6 percent of the selected dark clouds have associated IRAS sources with IRAS colors typical of pre-main-sequence stars. A study of the energy distributions obtained from JHKLM photometry and IRAS flux densities give an identification of these IRAS sources. Thirteen sources have been classified as new low-mass protostellar objects and T Tauri-type stars with nebular surrounding material disks, while four IRAS sources have no evidence of near-IR excesses and appear to be similar to post T Tauri stars in which the nebular disks are probably absent or optically thin. 17 refs.

Ultraviolet and Optical Observations of HDE 245770/ A 0535+26 System during an X-Ray Flare

We present high and low dispersion UV spectra of HDE 245770,which is the optical counterpart of the recurrent transient X-ray pulsar A 0535+26,during a decay of an X-ray flare. UBV photometric measurements and medium dispersion optical spectra were simultaneously obtained.

Tircam:A mid-infrared camera for ground-based astronomy

A mid-infrared (8–22 μm) camera, equipped with a Hughes hybrid bulk Si:As array detector of 10×64 pixels was developed for the 1.5 m Italian Infrared Telescope (TIRGO). The instrument was used for narrow- band 8–14 μm high-background astronomical observations. Here we present a short description of the camera, including its fast readout electronics and its optical design. When used at TIRGO, the camera has a pixel scale of 1.23 arcsec/pix. From the observations of infrared standard stars we derived a noise equivalent flux density (NEFD) that, for all the filters, is in the range 0.5–0.7 Jy×arcsec-2×min-1/2 and a point spread function (PSF) of the order of 3 arcsec(FWHM). Mosaics of the extended sources Mars at 8.8, 9.8, and 12.5 μm, and of the star forming region Orion BN-KL Nebula at 12.5 μm, are shown. The camera performances are also illustrated on the basis of the image of the post-AGB source CRL618.

TIRCAM: a mid-IR camera for astronomical imaging

We present the main characteristics of a new mid-IR camera, TIRCAM, operating at the 1.5 m Italian Infrared Telescope.

Dust Envelopes and IR Excesses in a Sample of RS CVn-Type Binaries

In recent years, we have been studying the energy distribution of RS CVn binaries from UV to far IR wave lengths, in order to derive general properties of the systems and to better understand their evolutionary scenario, including the history of mass loss (Busso et al., 1987, 1988). In this framework, we have so far analyzed, at different level of accuracy, a total of about 60 sources, among which 30 have been the object of detailed studies, on the basis of broad band photomertic observations from 0.35 to 60 µm, using ground-based telescopes (mainly at La Silla, ESO) and IRAS-PSC information. For these 30 binaries, the quasi-periodic variations due to the presence of photospheric spots have been carefully subtracted, to derive the energy distributions of the unperturbed systems.

IRAS and Near Infrared Observations of Peculiar Nebulosities

We used the IRAS survey to search for IR emission from 95 peculiar nebulosities with CO emission. Fifty-two IRAS sources are associated with them. We discuss the nature of the sources on the basis of their IRAS color-color diagram and of near-IR observations.

Radio and Infrared Observations of CYG OB2 No. 5

VLA measurements of the 6 cm flux of Cyg OB2 No. 5 reveal it has increased by a factor of 4 between 1980 and 1984. From 1983 July to 1984 September the 6 cm flux has slowly increased from 5.8 to 7.3 mJy. During 1984 September the 6 and 2 cm fluxes were measured in 7 occasions. During this month no variability was detected at the 10 percent level and the spectral index was 0.1±0.1. The 6.6-day variability found at 2.2 μm originates from the eclipsing of the contact binary system. There is no evidence of IR variability from the emission originating in the ionized wind. It is yet unclear if the radio emission has a thermal or a nonthermal nature. A model in terms of the ejection of a dense shell (superposed on a steady stellar wind) is discussed.

Infrared photometry of the x-ray stars in cygnus OB2(VI Cygni): Preliminary results

The Cygnus OB2 association (also known as VI Cygni), has long been known as a heavly obscured group of very luminous stars. The association is very young and includes several giants and supergiants earlier than 07, one of which is an 03If (Walborn,1973).