Observational Constraints on the Formation and Evolution of Binary Stars

By R. White, A. Texas, Austin, U. California, Los Angeles. 2001

444 citations recorded by the source corpus.

We present a high spatial resolution multiwavelength survey of 44 young binary star systems in Taurus-Auriga with separations of 10-1000 AU. These observations, which were obtained using the Hubble Space Telescope and the NASA Infrared Telescope Facility, quadruple the number of close (less than 100 AU) binary stars with spatially resolved measurements from 0.3 to 2.2 μm and are the first 3.6 μm measurements for the majority of the companion stars in the sample. Masses and ages are estimated for the components observed at optical wavelengths. The relative ages of binary star components are more similar than the relative ages of randomly paired single stars within the same star-forming region. This is the first statistically significant evidence for coeval formation. Only one of the companion masses is substellar, from which we conclude that the apparent overabundance of T Tauri star companions relative to main-sequence star companions is not due to a wealth of substellar secondaries that would have been missed in main-sequence surveys. The circumstellar environments of binary star systems are studied in this work through three diagnostics: the infrared color K-L, the ultraviolet excess ΔU, and Hα emission. Several conclusions are drawn. First, the mass accretion rates for primary stars are similar to single stars, which suggests that companions as close as 10 AU have little effect on the mass accretion rate. Second, although most classical T Tauri star binaries retain both a circumprimary and a circumsecondary disk, there are several systems with only a circumprimary disk. Systems with only a circumsecondary disk are rare. This suggests that circumprimary disks survive longer than circumsecondary disks. Third, primary stars accrete at a higher rate, on average, than secondary stars. This is most likely because of their larger stellar mass, since the mass accretion rates for both single and binary T Tauri stars exhibit a moderate mass dependence. Fourth, approximately 10% of T Tauri binary star components have very red near-infrared colors (K-L > 1.4) and unusually high mass accretion rates. This phenomenon does not appear to be restricted to binary systems, however, since a comparable fraction of single T Tauri stars exhibit the same properties. These high accretion rate stars are probably not at an earlier stage of evolution, as has been proposed. Their semblance of younger protostars at optical and infrared wavelengths is most likely because of their similar high levels of accretion, which are above the norm for T Tauri stars, and not because of similar ages. The stellar and circumstellar properties are also used to trace indirectly the evolution of circumbinary material. In contrast to single T Tauri stars, which have disk dissipation timescales comparable to their ages, the disk dissipation timescales for binary T Tauri stars are ~10 times less than their ages. Replenishment of the inner circumstellar disks may be necessary to explain the continuing disk accretion in these systems. The longer disk lifetimes of circumprimary disks, despite their higher depletion rates, suggest that circumprimary disks are being preferentially replenished, possibly from a circumbinary reservoir with low angular momentum relative to the binary. Further support for circumbinary reservoirs comes from the observed correlated presence of circumprimary and circumsecondary disks for binaries with separations of less than ~200 AU. The presence of disks appears uncorrelated for wider binaries. Additionally, binaries with separations of less than ~100 AU exhibit a higher fraction of high mass ratio (ms/mp) pairs than wider binaries. These separation-dependent properties can be explained if the components are being replenished from a common circumbinary reservoir with low angular momentum. The components of the closest pairs are expected to be more equally replenished than the widest pairs, which consequently sustains both disks and drives their mass ratios toward unity. Overall, the results of this study corroborate previous work that suggests that fragmentation is the dominant binary star formation mechanism in Taurus-Auriga; disk instabilities and capture seem unlikely.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/19fd80f81e676629017210696b23c09a7caa2e2a

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Citations in the corpus

Dust filtration at gap edges: Implications for the spectral energy distributions of discs with embedded planets (2006, background): “Both GM Aur and DM Tau are Classical T Tauri stars, with estimated accretion rates on to the stellar photosphere variously estimated at Ṁ ≈ 10−9 M⊙yr −1 to 10−8 M⊙yr −1 (Gullbring et al. 1998; Hartmann et al. 1998; White & Ghez 2001).”
Accretion in the ρ-Ophiuchi pre-main sequence stars (2006, methodology): “Based on the near and mid-IR colors, the objects were divided in Class I (accreting protostars), Class II and tentative Class II (pre-main sequence stars with IR excess typical of disks, like classical T Tauri stars or CTTS), and Class III/tentative Class III (objects with colors typical of stellar ”
GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS (2009, background): “Some nearby star-forming regions, such as Taurus-Auriga, have been the subject of detailed multiplicity surveys (e.g., White & Ghez 2001), but more distant and more heavily embedded regions have not been similarly studied.”
Accretion onto Pre-Main-Sequence Stars (2016, background): “The results from these surveys have since been adapted to broadband imaging surveys that include U-band (or u-band) photometry (e.g., Hartmann et al. 1998, White & Ghez 2001, Robberto et al. 2004, Sicilia-Aguilar et al. 2010, Rigliaco et al. 2011).”
Accretion Rates in Herbig Ae stars (2006, unknown): “Results can be found, e.g., in Gullbring et al. 1998, Muzerolle et al. (1998, 2003, 2005), White and Ghez (2001), Natta et al. (2004, 2006), Mohanty et al. (2005).”
On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga (2004, background): “These comparisons imply T Tauri ages of a few times 106 yr, with no statistically significant difference between the H-R diagram locations of class II and class III stars (Kenyon & Hartmann 1995; White & Ghez 2001; Briceño et al. 2002).”
Stellar Multiplicity (2013, unknown): “Nonetheless, in the absence of complete spectroscopic follow-up campaigns (e.g., Hartigan & Kenyon 2003, White & Ghez 2001), this is the only available tool in most cases.”
THE ROLE OF MULTIPLICITY IN DISK EVOLUTION AND PLANET FORMATION (2011, background): “Previous surveys have found some evidence for a correlation between binarity and disk properties (Jensen et al. 1996; Ghez et al. 1997; White & Ghez 2001; Cieza et al. 2009; Duchêne 2010), but the resolution limits of these surveys only included a restricted range of binary separations, with many…”
TRANSITIONAL DISKS AS SIGNPOSTS OF YOUNG, MULTIPLANET SYSTEMS (2011, unknown): “10−8 M⊙ yr −1 (White & Ghez 2001, Johns-Krull & Gafford 2002, Andrews et al. 2011); 4.”
THE DISK POPULATION OF THE TAURUS STAR-FORMING REGION (2009, background): “′′3 companion FW Tau C, which is known to have a disk (White & Ghez 2001).”
X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud (2006, unknown): “Using the accretion rate Ṁ ≈ (3–6) × 10−8 M yr−1 for T Tau (White & Ghez 2001; Calvet et al. 2004) we obtain n2 = (1.1–2.2) × 1011/ f (Güdel et al. 2007c).”
A Survey and Analysis of Spitzer Infrared Spectrograph Spectra of T Tauri Stars in Taurus (2006, methodology): “These stars might be experiencing an episodic phase of high accretion, which could be accompanied by a larger amount of extinction (White & Ghez 2001).”
Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga (2002, methodology): “Using the sample of single T Tauri stars listed in White & Ghez ( 2001 ) with spectral types hotter than M5 , 63% are classical T Tauri stars ( 30 of 48 stars ) .”
The Magnetic Fields of Classical T Tauri Stars (2007, background): “ForDGTau, DHTau, andTTauwe take these values from White & Ghez (2001).”