Infrared Excesses in T Tauri Stars and Related Objects

We have made multicolor photometric observations, over the range of wavelength from 0 36 ~ in the ultraviolet to 5 0 ~ in the infrared, on thirty-three T Tauri-like stars. This photometry confirms the infrared excess previously reported. It also shows irregular light variations in all UBVRIJHKLM bands. Most of the infrared excesses in these stars remain after correction for interstellar extinction. The corrected photometry, converted into fluxes, was used to compute total luminosities; they range from 4 9 to 828 times the solar luminosity These luminosities, combined with the adopted effective temperatures, are used to estimate masses and ages. The former range from 1.8 to 7.3 M0; the latter range from 16000 to 3 9 X 106 years. The luminosities and effective temperatures are also used to con- struct the H-R diagram for T Tauri-like stars. They lie well above the main sequence. The infrared excesses can be explained by two mode]s. If the infrared luminosity is many times the visual luminosity, then a thick circumstellar dust cloud absorbs the visual radiation and reradiates in the infrared the energy produced by the parent star. If the infrared luminosity is a few times the visual luminosity, then the infrared excess is the result of the heating of the outer stellar wind by the absorption of the stellar cosmic rays. I. INTRODUCTION The spectra of T Tauri stars show absorption lines that are abnormally wide, even for dwarfs; thus early workers located them on the main sequence (see, e.g., Joy 1945; Greenstein and Aller 1947). Color-magnitude diagrams of clusters containing T Tauri- like stars provided the first indication that they might lie above the main sequence (Walker 1956, 1957, 1959). Multicolor photometry of T Tauri stars and related objects by Mendoza (1966; "Paper I") shows that all the programs stars exhibit infrared excess, some of which are very large. A plausible interpretation is that these objects are more luminous than indicated by their color-magnitude diagrams (see below). We have made additional multicolor photometry of some of the T Tauri stars and related objects reported in Paper I, and of a few other T Tauri-like stars listed in Herbig's review paper (1962). All the observations were made between January, 1965, and June, 1967, with the photometric equipment as described by Johnson and Mitchell (1962) and by Low and Johnson (1964), attached to the 28-inch and 60-inch photometric telescopes of the Lunar and Planetary Laboratory. II. THE OBSERVATION