THE ASTROPHYSICAL JOURNAL, 545 :1034È1043, 2001 December 202001. The American Astronomical Society. All rights reserved. Printed in U.S.A.(DYNAMICAL MASSES OF T TAURI STARS AND CALIBRATION OFPREÈMAIN-SEQUENCE EVOLUTIONM. SIMONDepartment of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800 ; msimon=sbast1.ess.sunysb.eduANDA. DUTREY AND S. GUILLOTEAUInstitut de Radio Astronomie 300 Rue de la Piscine, F-38406 Saint Martin FranceMillimetrique, dÏHe`res,Received 2000 April 4 ; accepted 2000 August 18ABSTRACTWe have used the high sensitivity and resolution of the IRAM interferometer to produce subarcsecond12CO J \ 2È1 images of nine protoplanetary disks surrounding T Tauri stars in the Taurus-Aurigacloud (seven singles and two binaries). The images demonstrate the disks are in Keplerian rotationaround their central stars. Using the least-square Ðt method described in the 1998 work by Guilloteau &Dutrey, we derive the diskÏs properties, in particular its inclination angle and rotation velocity, hence thedynamical mass. Since the disk mass is usually small, this is a direct measurement of the stellar mass.Typically, we reach an internal precision of 10% in the determinations of stellar mass. The overall accu-racy is limited by the uncertainty in the distance to a speciÐc star. In a distance-independent way, wecompare the derived masses with theoretical tracks of preÈmain-sequence evolution. Combined with themean distance to the Taurus region (140 pc), for stars with mass close to 1 our results tend to favorM_,the tracks with cooler photospheres (higher masses for a given spectral type). We Ðnd that in UZ Tau E,the disk and the spectroscopic binary orbit appear to have di†erent inclinations.Subject headings: binaries: close È circumstellar matter È radio lines: stars È stars: individual(BP Tauri, CY Tauri, DL Tauri, DM Tauri, GG Tauri, GM Aurigae, LkCa 15,MWC 480, UZ Tauri) È stars: preÈmain-sequence È stars: variables: other1. INTRODUCTIONNearly all of our knowledge about the masses and ages oflow-mass young stars comes from their location in the H-Rdiagram relative to theoretical calculations of stellar evolu-tion to the main sequence. Despite considerable advancesover the past 5È10 years in understanding the structure andatmospheres of stars of mass M \ 1 comparison of theM_,currently available predicted evolutionary paths of youngstars shows obvious di†erences. Empirical tests of the calcu-lations have not been possible until recently because astron-omers have not had independent measurements of eitherthe mass or age of a young star. This situation is changingrapidly. One way to test the calculated tracks is to investi-gate whether they yield the same ages for stars expected tobe coeval on physical grounds. Hartigan, Strom, & Strom(1994), Casey et al. (1998), and White et al. (1999) haveapplied this test to wide binaries, the TY CrA system, andthe GG Tau system, respectively, using tracks available atthe time. Over a mass range extending down to the browndwarfs, they found signiÐcant di†erences in the extent towhich the several theoretical calculations satisfy thecoevality requirement.The capability of millimeter-wave interferometers toresolve the spectral line emission of the outer disks of preÈmain-sequence (PMS) stars o†ers the possibility to maptheir rotation. Since the disk mass is usually very smallcompared to the mass of the star, this provides the means tomeasure the stellar mass dynamically (e.g., Dutrey, Guillo-teau, & Simon 1994, hereafter DGS94 ; Guilloteau &Dutrey 1998, hereafter GD98). We use this technique toobtain new measurements of the mass of Ðve single PMSstars and one PMS binary. Combined with our previousmeasurements of the PMS single GM Aur and the binaryGG Tau (Dutrey et al. 1998; Guilloteau, Dutrey, & Simon1999), the measured stellar masses span the range D2to0.5We use the results to test the theoretical calculations ofM_.PMS evolution. Section 2 describes the sample of stars andthe interferometric observations. Section 3 summarizes theanalysis and presents the measured masses and relatedparameters. Section 4 compares the measured masses withthose implied by location of the stars in the H-R diagramrelative to the tracks calculated by dÏAntona & Mazzitelli(1997, hereafter DM97),1 Bara†e et al. (1998, hereafterBCAH), Palla & Stahler (1999, hereafter PS99), and Siess,Dufour, & Forestini (2000, hereafter SDF).22. SAMPLE OF STARS AND INTERFEROMETEROBSERVATIONS2.1. Sample of StarsAll the stars studied are in Taurus-Auriga (Table 1). Weobtained new interferometric observations in the 12COJ \ 2È1 line of the singles CY Tau, DL Tau, DM Tau,LkCa 15, and MWC 480 (HD 31648), and the spectroscopicbinary UZ Tau E (Mathieu, Martin, & Maguzzu 1996).They were selected because earlier interferometric obser-vations (Table 1, col. [5]) indicated that they were, or werelikely to be, associated with resolvable circumstellar disks.BP Tau was observed because its Hipparcos distance,56 ^ 14 pc (Favata et al. 1998), is very di†erent from the 140pc average distance to the Taurus star-forming region(Kenyon, Dobryzycka, & Hartmann 1994), suggesting thatit is much older than previously thought (see also Bertout,1 See also http://venus.mporzio.astro.it/Ddantona/.2 See also http://www-laog.obs.ujf-grenoble.fr/activites/starevol/evol.html.1034T TAURI STARS AND PREÈMAIN-SEQUENCE EVOLUTION 1035TABLE 1PARAMETERS OF PROGRAM STARSTeffReferencesa ReferencesbName Spectral Type L*/L_(K) (CO) (L*, Teff)(1) (2) (3) (4) (5) (6)SinglesMWC 480........ A4 11.5 8460 1 1LkCa 15 .......... K5 0.74 4350 2 . . .DL Tau .......... K7 0.68 4060 3 2GM Aur.......... K7 0.74 4060 4 3BP Tau........... K7 0.93 4060 . . . 4DM Tau ......... M1 0.25 3720 5 . . .CY Tau .......... M1 0.47 3720 3 . . .BinariesGG Tau Aa...... K7 0.84 4060 6 5GG Tau Ab...... M0.5 0.71 3800 . . . . . .UZ Tau E........ M1 1.60 3720 3, 7 . . .a References to col. (5): (1) Mannings & Sargent 1997; (2) Duvert et al. 2000 ; (3) Dutrey etal. 1996; (4) Dutrey et al. 1998; (5) Guilloteau & Dutrey 1998 ; (6) Guilloteau, Dutrey, &Simon 1999 ; (7) Jensen, Koerner, & Mathieu 1996.b References to col. (6): (1) from Malfait et al. 1998 and this work, and spectral typeL*from C. Grady, 1999, private communication ; (2) from Hartigan, Edwards, & GhandourL*1995; (3) spectral type and from Gullbring et al. 1998 ; (4) see Favata et al. 1998 and ° 4.1;L*(5) and spectral type from White et al.
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