We present a large, comprehensive survey of rovibrational CO line emission at 4.7 {$μ$}m from 69 protoplanetary disks, obtained with CRIRES on the ESO Very Large Telescope at the highest available... Show moreWe present a large, comprehensive survey of rovibrational CO line emission at 4.7 {$μ$}m from 69 protoplanetary disks, obtained with CRIRES on the ESO Very Large Telescope at the highest available spectral resolving power (R = 95,000, {$Delta$}v = 3.2 km s$^{-1}$). The CO fundamental band ({$Delta$}v = 1) is a well-known tracer of warm gas in the inner, planet-forming regions of gas-rich disks around young stars, with the lines formed in the super-heated surfaces of the disks at radii of 0.1-10 AU. Consistent with earlier studies, the presence of 100-1000 K CO is found to be ubiquitous around young stars which still retain disks. Our high spectral resolution data provide new insight into the kinematics of the inner disk gas. The observed line profiles are complex and reveal several different components. Pure double-peaked Keplerian profiles are surprisingly uncommon in our sample, beyond the frequency expected based on disk inclination. The majority of the profiles are consistent with emission from a disk plus a slow (few km s$^{-1}$) molecular disk wind. This is evidenced by analysis of different classes as well as an overall tendency for line profiles to have excess emission on their blue side. The data support the notion that thermal molecular winds are common for young disks. Thanks to the high spectral resolution, narrow absorption lines and weak emission lines from isotopologues and from vibrationally excited levels are readily detected. In general, $^{13}$CO lines trace cooler gas than the bulk $^{12}$CO emission and may arise from further out in the disk, as indicated by narrower line profiles. A high fraction of the sources show vibrationally excited emission (~{}50%) which is correlated with accretion luminosity, consistent with ultraviolet fluorescent excitation. Disks around early-type Herbig AeBe stars have narrower line profiles, on average, than their lower-mass late-type counterparts, due to their increased luminosity. Evolutionary changes in CO are also seen. Removal of the protostellar envelope between class I and II results in the disappearance of the strong absorption lines and CO ice feature characteristic of class I spectra. However, CO emission from class I and II objects are similar in detection frequency, excitation, and line shape, indicating that inner disk characteristics are established early. Show less
In this work, we introduce the use of H I Pfund {$β$} (Pf{$β$} 4.6538 {$μ$}m) as a tracer of mass accretion from protoplanetary disks onto young stars. Pf{$β$} was serendipitously observed in... Show moreIn this work, we introduce the use of H I Pfund {$β$} (Pf{$β$} 4.6538 {$μ$}m) as a tracer of mass accretion from protoplanetary disks onto young stars. Pf{$β$} was serendipitously observed in NIRSPEC and CRIRES surveys of CO fundamental emission, amounting to a sample size of 120 young stars with detected Pf{$β$} emission. Using a subsample of disks with previously measured accretion luminosities, we show that Pf{$β$} line luminosity is well correlated with accretion luminosity over a range of at least three orders of magnitude. We use this correlation to derive accretion luminosities for all 120 targets, 65 of which are previously unreported in the literature. The conversion from accretion luminosity to accretion rate is limited by the availability of stellar mass and radius measurements; nevertheless, we also report accretion rates for 67 targets, 16 previously unmeasured. Our large sample size and our ability to probe high extinction values allow for relatively unbiased comparisons between different types of disks. We find that the transitional disks in our sample have lower than average Pf{$β$} line luminosities, and thus accretion luminosities, at a marginally significant level. We also show that high Pf{$β$} equivalent width is a signature of transitional disks with high inner disk gas/dust ratios. In contrast, we find that disks with signatures of slow disk winds have Pf{$β$} luminosities comparable to those of other disks in our sample. Finally, we investigate accretion rates for stage I disks, including significantly embedded targets. We find that stage I and stage II disks have statistically indistinguishable Pf{$β$} line luminosities, implying similar accretion rates, and that the accretion rates of stage I disks are too low to be consistent with quiescent accretion. Our results are instead consistent with both observational and theoretical evidence that stage I objects experience episodic, rather than quiescent, accretion. Show less
We find a trend between the mid-infrared HCN/H$_{2}$O flux ratio and submillimeter disk mass among T Tauri stars in Taurus. While it may seem puzzling that the molecular emission properties of the... Show moreWe find a trend between the mid-infrared HCN/H$_{2}$O flux ratio and submillimeter disk mass among T Tauri stars in Taurus. While it may seem puzzling that the molecular emission properties of the inner disk ({lt}few AU) are related to the properties of the outer disk (beyond ~{}20 AU) probed by the submillimeter continuum, an interesting possible interpretation is that the trend is a result of planetesimal and protoplanet formation. Because objects this large are decoupled from the accretion flow, when they form, they can lock up water (and oxygen) beyond the snow line, thereby enhancing the C/O ratio in the inner disk and altering the molecular abundances there. We discuss the assumptions that underlie this interpretation, a possible alternative explanation, and related open questions that motivate future work. Whatever its origin, understanding the meaning of the relation between the HCN/H$_{2}$O ratio and disk mass is of interest as trends like this among T Tauri disk properties are relatively rare. Show less
We find a trend between the mid-infrared HCN/H$_{2}$O flux ratio and submillimeter disk mass among T Tauri stars in Taurus. While it may seem puzzling that the molecular emission properties of the... Show moreWe find a trend between the mid-infrared HCN/H$_{2}$O flux ratio and submillimeter disk mass among T Tauri stars in Taurus. While it may seem puzzling that the molecular emission properties of the inner disk ({lt}few AU) are related to the properties of the outer disk (beyond ~{}20 AU) probed by the submillimeter continuum, an interesting possible interpretation is that the trend is a result of planetesimal and protoplanet formation. Because objects this large are decoupled from the accretion flow, when they form, they can lock up water (and oxygen) beyond the snow line, thereby enhancing the C/O ratio in the inner disk and altering the molecular abundances there. We discuss the assumptions that underlie this interpretation, a possible alternative explanation, and related open questions that motivate future work. Whatever its origin, understanding the meaning of the relation between the HCN/H$_{2}$O ratio and disk mass is of interest as trends like this among T Tauri disk properties are relatively rare. Show less
