CDROM/APJS/V101/P117 Pre-Main-Sequence Evolution in Taurus-Auriga (Kenyon+ 1995) ================================================================================ Pre-Main-Sequence Evolution in the Taurus-Auriga Molecular Cloud Scott J. Kenyon & Lee Hartmann <1995, ApJS, 101, 117> =1995ApJS..101..117K ================================================================================ Abstract: This paper analyzes optical and infrared photometry of pre-main- sequence stars in the Taurus-Auriga molecular cloud. More than half of the stars in our sample have excess near-infrared emission. The near-infrared excesses correlate very well with other measures of activity, such as Halpha emission, ultraviolet excess emission, millimeter continuum emission, and the presence of reflection nebulae and molecular outflows. The infrared colors and the ratio of far-infrared to bolometric luminosity display a smooth progression from the most deeply embedded protostars to optically visible T Tauri stars. Infalling envelope models account for the colors of protostars; simple disk models similarly reproduce the colors of many T Tauri stars. Both the stellar birth line and a 10^5 yr isochrone provide a reasonable upper envelope to the luminosity distribution of optically visible stars in the H-R diagram. Only a few stars in the cloud have apparent ages exceeding 2-3 x 10^6 yr, as derived from detailed stellar evolution calculations. The distribution of stars in the H-R diagram indicates that the cloud has formed stars at a roughly constant rate for the past 1-2 x 10^6 yr. Analyses of the J- and K-luminosity functions support this conclusion. Within the uncertainties, the observed mass distribution for optically visible stars agrees with a Miller-Scalo initial mass function. Source statistics imply a lifetime of 1-2 x 10^5 yr for the typical protostar in Taurus-Auriga. There is no evidence, however, that these sources lie on the stellar birth line. Indeed, the protostellar luminosity function is essentially identical to the luminosity function derived for optically visible T Tauri stars in the cloud. These results provide some support for the evolutionary sequence -- embedded protostar -> T Tauri star with a circumstellar disk -> T Tauri star without a circumstellar disk -- currently envisioned in standard models of low-mass star formation. Source statistics and infrared color-color diagrams demonstrate that pre-main-sequence stars develop bluer colors and display less evidence for circumstellar material with time. The data show little evidence, however, for the luminosity evolution expected along the proposed evolutionary sequence. Time-dependent accretion during the infall phase may account for the low luminosity of Taurus-Auriga protostars; this hypothesis requires more tests. Keywords: infrared: stars -- ISM: clouds -- stars: evolution -- stars: luminosity function, mass function -- stars: pre-main-sequence Description: Tables A1-A2 list average V and K magnitudes and broadband optical and near-infrared colors for T Tauri stars in the Taurus-Auriga cloud. The quoted errors are 1 sigma dispersions from the average values for objects with 2 or more measurements at V, K, or the appropriate color. For convenience, the authors quote dispersions of 0.00 for objects with only a single measurement. The last columns of Tables A1-A2 list the number of V, K, and N measurements used to compute the average values. The number of data points used to determine average colors is usually close to the number of V or K measurements. Table A3 lists IRAS colors for the Taurus-Auriga sample. For each IRAS source, the authors compiled fluxes from version 2 of the Point Source Catalog, IRAS ADDSCANs, and the IRAS Serendipitous Survey Catalog and averaged fluxes for sources appearing in 2 or 3 catalogs (see section 2 of the printed paper). The authors adopted flux zero points of Fnu (12 um) = 28.3 Jy, Fnu (25 um) = 6.73 Jy, Fnu (60 um) = 1.19 Jy, and Fnu (100 um) = 0.43 Jy to compute IRAS magnitudes and then derived colors using average K magnitudes from Table A2. In some cases, two or more pre-main-sequence stars fall in a typical IRAS beam. The authors summed the K flux of the individual objects to compute a combined K magnitude and color for these IRAS sources. These IRAS colors assume _no_ color correction for the IRAS flux. Table A4 lists various quantities derived from published spectra and the photometry in Tables A1-A3. Infrared colors and the ratio of far-IR to bolometric luminosity set the spectral energy distribution class, SED. The optical spectral type usually was taken from the literature (Herbig & Bell 1988) or the authors own work. The effective temperature, Teff, is based on compilations by Schmidt-Kaler (1982) and Straizys (1992). The authors estimated optical extinctions, A_V, from comparisons between the observed optical or infrared colors and colors for normal main sequence stars in Table A5. The authors adopted Bessell & Brett's (1988) extinction curve to derive A_V from the optical color excess and to derive the extinction at 1.25 um, A_J. The stellar luminosity, L_J, follows from the observed J magnitude, the extinction, and an appropriate bolometric correction from Table A5 for a distance of d = 140 pc. The 7-135 um luminosity, L_FIR, and the bolometric luminosity, L_b, are both integrations over the reddening-corrected flux distribution. The 7-135 um luminosity is quoted as an upper limit for sources not detected by IRAS. Lower limits on L_b are quoted for sources with incomplete photometry. Table A5 lists adopted broadband colors for main sequence stars. For the optical colors, this list is based on data compiled by Johnson (1966; U-B, B-V, V-R_J, and V-J_C), Schmidt-Kaler (1982; U-B and B-V), and Bessell (1990a,b; U-B, B-V, V-R_C, and V-I_C). Bessell & Brett (1988) contains the most comprehensive list of main sequence IR colors. The authors supplemented their Table II with colors from Johnson (1966) for early-type main sequence stars. Johnson (1966) contains the best list of K-N colors for main sequence stars. To complement these data, the authors compiled V-[12] colors using stars selected from the Third Catalog of Nearby Stars (Gliese & Jahreiss 1979). The authors extracted 12 um fluxes from version 2 of the IRAS Point Source Catalog, color-corrected the fluxes assuming a color temperature equal to the stellar effective temperature, and computed a V-[12] color assuming a 12 um zero point of 28.3 Jy. The tabulated color is the median color. The tabulated visual bolometric corrections, BC_V = M_bol - M_V, were used to derive absolute J luminosities, L_J. The authors adopted BC_V from Schmidt-Kaler (1982; also Straizys 1992) for stars with spectral types earlier than K6; the authors integrated the energy distributiuon over wavelength to derive BC_V for for later spectral types. References to the Documentation: Bessell, M. S. 1990a, A&AS, 83, 357 Bessell, M. S. 1990b, PASP, 102, 1181 Bessell, M. S., & Brett, J. M. 1988, PASP, 100, 1134 Gliese, W., & Jahreiss, H. 1979, A&AS, 38, 423 Herbig, G. H., & Bell, K. R. 1988, Lick Obs. Bull., No. 1111 Johnson, H. L. 1966, ARA&A, 4, 193 Schmidt-Kaler, Th. 1982, in Landolt-Bornstein Tables, Springer, p. 454 Straizys, V. 1992, Multicolor Stellar Photometry, Tucson, Pachart File Summary: -------------------------------------------------------------------------------- File Name Lrecl Records Explanations -------------------------------------------------------------------------------- tablea1.dat 73 287 Mean optical photometry tablea2.dat 98 289 Mean near-IR photometry tablea3.dat 66 158 Far-IR colors tablea4.dat 76 190 Luminosities and extinctions tablea5.dat 94 55 Colors for main-squence stars table.tex 273 1143 AASTeX version of tables A1-A5 -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-14 A14 --- Name Star name 15-20 F6.2 mag V []? Average V magnitude 21-25 F5.2 mag e_V *[]? V error 26-31 F6.2 mag U-B []? Average U-B color 32-36 F5.2 mag e_U-B *[]? U-B error 37-42 F6.2 mag B-V []? Average B-V color 43-47 F5.2 mag e_B-V *[]? B-V error 48-53 F6.2 mag V-R []? Average V-R color 54-58 F5.2 mag e_V-R *[]? V-R error 59-64 F6.2 mag R-I []? Average R-I color 65-69 F5.2 mag e_R-I *[]? R-I error 70-73 I4 --- N_V *[]?=0 Number of V measurements for average -------------------------------------------------------------------------------- Notes for file: tablea1.dat -------------------------------------------------------------------------------- e_V, e_U-B, e_B-V, e_V-R, e_R-I: The quoted errors are 1 sigma dispersions from the average values for objects with 2 or more measurements. For convenience the dispersions are 0.00 for objects with only a single measurement (N_V = 1). N_V: The number of data points used to determine average colors is usually close to the number of V measurements -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-14 A14 --- Name Star name 15-20 F6.2 mag K []? Average K magnitude 21-25 F5.2 mag e_K *[]? K error 26-31 F6.2 mag J-K []? Average J-K color 32-36 F5.2 mag e_J-K *[]? J-K error 37-42 F6.2 mag H-K []? Average H-K color 43-47 F5.2 mag e_H-K *[]? H-K error 48-53 F6.2 mag K-L []? Average K-L color 54-58 F5.2 mag e_K-L *[]? K-L error 59-64 F6.2 mag K-M []? Average K-M color 65-69 F5.2 mag e_K-M *[]? K-M error 70-75 F6.2 mag K-N []? Average K-N color 76-80 F5.2 mag e_K-N *[]? K-N error 81-86 F6.2 mag K-Q []? Average K-Q color 87-91 F5.2 mag e_K-Q *[]? K-Q error 92-95 I4 --- N_K *[]?=0 Number of K measurements for average 96-98 I3 --- N_N []?=0 Number of N measurements for average -------------------------------------------------------------------------------- Notes for file: tablea2.dat -------------------------------------------------------------------------------- e_K, e_J-K, e_H-K, e_K-L, e_K-M, e_K-N, e_K-Q: The quoted errors are 1 sigma dispersions from the average values for objects with 2 or more measurements. For convenience the dispersions are 0.00 for objects with only a single measurement (N_V = 1). N_K: The number of data points used to determine average colors is usually close to the number of K measurements -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-38 A38 --- Name Star names 39-45 F7.2 mag K-12 []? K-12 um color 46-52 F7.2 mag K-25 []? K-25 um color 53-59 F7.2 mag K-60 []? K-60 um color 60-66 F7.2 mag K-100 []? K-100 um color -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1-14 A14 --- Name Star name 15-18 A4 --- SED Spectral energy distribution class 19 1X --- --- Blank 20-24 A5 --- Sp Spectral type 25-30 I6 K Teff []? Effective temperature 31-36 F6.2 --- A_V []? Optical extinction 37-42 F6.2 --- A_J []? Extinction at 1.25 um 43-48 F6.2 --- L_J *[]? Stellar luminosity 49 1X --- --- Blank 50 A1 --- l_L_FIR *[< ] L_FIR limiting character 51-55 F5.2 --- L_FIR []? 7-135 um luminosity 56 1X --- --- Blank 57 A1 --- l_L_b *[> ] L_b limiting character 58-62 F5.2 --- L_b []? Bolometric luminosity 63 1X --- --- Blank 64 A1 --- l_L_Jb [< ] L_Jb limiting character 65-69 F5.2 --- L_Jb []? L_J/L_b ratio 70 1X --- --- Blank 71 A1 --- l_L_FIRb [< ] L_FIRb limiting character 72-76 F5.2 --- L_FIRb []? L_FIR/L_b ratio -------------------------------------------------------------------------------- Notes for file: tablea4.dat -------------------------------------------------------------------------------- L_J: The stellar luminosity, L_J, follows the J magnitude, the extinction and an appropriate bolometric correction from Table A5 for a distance of d = 140 pc. l_L_FIR: Luminosity is an upper limit, "<", for sources not detected by IRAS. l_L_b: Luminosity is a lower limit, ">", for sources with an incomplete photometry. -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 A4 --- Sp Spectral type 5-10 I6 K Teff Effective temperature 11-16 F6.2 mag BC Bolometric correction 17-22 F6.2 mag U-V U-V color 23-28 F6.2 mag B-V B-V color 29-34 F6.2 mag V-R_C V-R_C color 35-40 F6.2 mag V-R_J V-R_J color 41-46 F6.2 mag V-I_C V-I_C color 47-52 F6.2 mag V-I_J V-I_J color 53-58 F6.2 mag V-J V-J color 59-64 F6.2 mag V-H V-H color 65-70 F6.2 mag V-K V-K color 71-76 F6.2 mag V-L V-L color 77-82 F6.2 mag V-M []? V-M color 83-88 F6.2 mag V-N []? V-N color 89-94 F6.2 mag V-12 []? V-12 um color -------------------------------------------------------------------------------- ================================================================================ (End) Lee Brotzman [ADS] 06-Nov-95