Dynamical Masses and Stellar Evolutionary Model Predictions of M-Stars

Abstract

In this era of Gaia and ALMA, dynamical stellar mass measurements provide benchmarks that are independent of observations of stellar characteristics and their uncertainties. These benchmarks can then be used to validate and improve stellar evolutionary models, which can lead to both imprecise and inaccurate mass predictions for pre-main-sequence, low-mass stars. We present the dynamical stellar masses derived from disks around three M-stars (FP Tau, J0432+1827, and J1100-7619) using ALMA observations of ${}^{12}$CO (J=2--1) and ${}^{13}$CO (J=2--1) emission. These are the first dynamical stellar mass measurements for J0432+1827 and J1100-7619 and the most precise measurement for FP Tau. Fiducial stellar evolutionary model tracks, which do not include any treatment of magnetic activity, agree with the dynamical measurement of J0432+1827 but underpredict the mass by $\sim$60\% for FP Tau and $\sim$80\% for J1100-7619. Possible explanations for the underpredictions include inaccurate assumptions of stellar effective temperature, undetected binarity for J1100-7619, and that fiducial stellar evolutionary models are not complex enough to represent these stars. In the former case, the stellar effective temperatures would need to be increased by $\sim$40K to $\sim$340K to reconcile the fiducial model predictions with the dynamically-measured masses. In the latter case, we show that the dynamical masses can be reproduced using results from stellar evolutionary models with starspots, which incorporate fractional starspot coverage to represent the manifestation of magnetic activity. Folding in low-mass M-stars from the literature and assuming that the stellar effective temperatures are imprecise but accurate, we find tentative evidence of a relationship between fractional starspot coverage and observed effective temperature for these young, cool stars.

37 pages (14 pages in the main document, 23 pages in the appendix), 35 figures, 5 tables. Accepted in ApJ (December 2020)

References in corpus (16)

• Array Programming with NumPy
• The Gaia mission
• Modules for Experiments in Stellar Astrophysics (MESA)
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties
• The Stellar Population of the Chamaeleon I Star-Forming Region
• Placing the spotted T Tauri star LkCa 4 on an HR diagram
• An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
• Older and Colder: The impact of starspots on pre-main sequence stellar evolution
• Empirical Tests of Pre-Main-Sequence Stellar Evolution Models with Eclipsing Binaries
• Dynamical Masses of Low Mass Stars in the Taurus and Ophiuchus Star Forming Regions
• ALMA observations of the kinematics and chemistry of disc formation
• High Precision Dynamical Masses of Pre-Main Sequence Stars with ALMA and Gaia
• The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
• An ALMA Dynamical Mass Estimate of the Proposed Planetary-mass Companion FW Tau C

Cited by in corpus (10)

• Gas Disk Sizes from CO Line Observations: A Test of Angular Momentum Evolution
• Mapping Protoplanetary Disk Vertical Structure with CO Isotopologue Line Emission
• Addressing Systematics in the Traceback Age of the $\beta$ Pictoris Moving Group
• The ALMA view of MP Mus (PDS 66): a protoplanetary disk with no visible gaps down to 4 au scales
• Orbital elements and individual component masses from joint spectroscopic and astrometric data of double-line spectroscopic binaries
• Chemical modeling of Orion Nebula Cluster disks: evidence for massive, compact gas disks with ISM-like gas-to-dust ratios
• exoALMA. VIII. Probabilistic Moment Maps and Data Products using Non-parametric Linear Models
• An SMA Survey of Chemistry in Disks around Herbig AeBe Stars
• PRODIGE -- Planet-forming disks in Taurus with NOEMA. I. Overview and first results for 12CO, 13CO, and C18O
• A Large Double-ring Disk around the Taurus M Dwarf J04124068+2438157