61 research outputs found
A Proper Motion Study of the Haro 6-10 Outflow: Evidence for a Subarcsecond Binary
We present single-dish and VLBI observations of an outburst of water maser
emission from the young binary system Haro 6-10. Haro 6-10 lies in the Taurus
molecular cloud and contains a visible T Tauri star with an infrared companion
1.3" north. Using the Very Long Baseline Array, we obtained five observations
spanning 3 months and derived absolute positions for 20 distinct maser spots.
Three of the masers can be traced over 3 or more epochs, enabling us to extract
absolute proper motions and tangential velocities. We deduce that the masers
represent one side of a bipolar outflow that lies nearly in the plane of the
sky with an opening angle of ~45\deg. They are located within 50 mas of the
southern component of the binary, the visible T Tauri star Haro 6-10S. The mean
position angle on the sky of the maser proper motions (~220\deg) suggests they
are related to the previously observed giant Herbig-Haro (HH) flow which
includes HH410, HH411, HH412, and HH184A-E. A previously observed HH jet and
extended radio continuum emission (mean position angle of ~190\deg) must also
originate in the vicinity of Haro6-10S and represent a second, distinct outflow
in this region. We propose that a yet unobserved companion within 150 mas of
Haro6-10S is responsible for the giant HH/maser outflow while the visible star
is associated with the HH jet. Despite the presence of H_2 emission in the
spectrum of the northern component of the binary, Haro6-10N, none of
outflows/jets can be tied directly to this young stellar object
Post-Outburst Observations of V1647 Ori: Detection of a Brief Warm, Molecular Outflow
We present new observations of the fundamental ro-vibrational CO spectrum of
V1647 Ori, the young star whose recent outburst illuminated McNeil's Nebula.
Previous spectra, acquired during outburst in 2004 February and July, had shown
the CO emission lines to be broad and centrally peaked-similar to the CO
spectrum of a typical classical T Tauri star. In this paper, we present CO
spectra acquired shortly after the luminosity of the source returned to its
pre-outburst level (2006 February) and roughly one year later (2006 December
and 2007 February). The spectrum taken in 2006 February revealed blue-shifted
CO absorption lines superimposed on the previously observed CO emission lines.
The projected velocity, column density, and temperature of this outflowing gas
was 30 km/s, 3^{+2}_{-1}E18 cm^{-2$, and 700^{+300}_{-100} K, respectively. The
absorption lines were not observed in the 2006 December and 2007 February data,
and so their strengths must have decreased in the interim by a factor of 9 or
more. We discuss three mechanisms that could give rise to this unusual outflow.Comment: 14 pages, 2 figures, accepted for publication in ApJ
Discovery of CO Gas in the Inner Disk of TW Hydrae
We report the detection of rovibrationally excited CO emission from the inner disk of the classical T Tauri star (cTTS) TW Hya. We observe ~6 × 1021 g of CO gas with a rotational temperature of 430 ± 40 K. The linearity of the excitation plot suggests that the CO is optically thin. Atypical for cTTSs, hot CO was not detected, implying that TW Hya has cleared its inner disk region out to a radial distance of ~0.5 AU. We discuss implications for the structure of the disk as it relates to replenishment and planet formation
Dust Stratification in Young Circumstellar Disks
We present high-resolution infrared spectra of four YSOs (T Tau N, T Tau S,
RNO 91, and HL Tau). The spectra exhibit narrow absorption lines of 12CO, 13CO,
and C18O as well as broad emission lines of gas phase12CO. The narrow
absorption lines of CO are shown to originate from the colder circumstellar
gas. We find that the line of sight gas column densities resulting from the CO
absorption lines are much higher than expected for the measured extinction for
each source and suggest the gas to dust ratio is measuring the dust settling
and/or grain coagulation in these extended disks. We provide a model of
turbulence, dust settling and grain growth to explain the results. The
techniques presented here allow us to provide some observationally-motivated
bounds on accretion disk alpha in protostellar systems
Near-Infrared Spectroscopic Study of V1647 Ori
We present new high-resolution infrared echelle spectra of V1647 Ori, the young star that illuminates McNeil\u27s nebula. From the start, V1647 Ori has been an enigmatic source that has defied classification, in some ways resembling eruptive stars of the FUor class and in other respects the EXor variables. V1647 Ori underwent an outburst in 2003 before fading back to its pre-outburst brightness in 2006. In 2008, it underwent a new outburst. In this paper we present high-resolution K-band and M-band spectra from the W. M. Keck Observatory that were acquired during the 2008 outburst. We compare the spectra to spectra acquired during the previous outburst and quiescent phases. We find that the luminosity and full width at half maximum power of Br-gamma increased as the star has brightened and decreased when the star faded indicating that these phases are driven by variations in the accretion rate. We also show that the temperature of the CO emission has varied with the stellar accretion rate confirming suggestions from modeling of the heating mechanisms of the inner disk (e.g. Glassgold et al. 2004). Finally we find that the lowest energy blue-shifted CO absorption lines originally reported in 2007 are no longer detected. The absence of these lines confirms the short-lived nature of the outflow launched at the start of the quiescent phase in 2006
The Gas/Dust Ratio of Circumstellar Disks: Testing Models of Planetesimal Formation
We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6–5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust columndensity ratio and disk inclination similar to that found by Rettig et al
Comet C/2004 Q2 (MACHHOLZ): Parent Volatiles, a Search for Deuterated Methane, and Constraint on the CH4 Spin Temperature
High-dispersion (l/dl ~ 25,000) infrared spectra of Comet C/2004 Q2
(Machholz) were acquired on Nov. 28-29, 2004, and Jan. 19, 2005 (UT dates) with
NIRSPEC at the Keck-2 telescope on Mauna Kea. We detected H2O, CH4, C2H2, C2H6,
CO, H2CO, CH3OH, HCN, and NH3 and we conducted a sensitive search for CH3D. We
report rotational temperatures, production rates, and mixing ratios (with
respect to H2O) at heliocentric distances of 1.49 AU (Nov. 2004) and 1.21 AU
(Jan. 2005). We highlight three principal results: (1) The mixing ratios of
parent volatiles measured at 1.49 AU and 1.21 AU agree within confidence
limits, consistent with homogeneous composition in the mean volatile release
from the nucleus of C/2004 Q2. Notably, the relative abundance of C2H6/C2H2 is
substantially higher than those measured in other comets, while the mixing
ratios C2H6/H2O, CH3OH/H2O, and HCN/H2O are similar to those observed in
comets, referred to as "organics-normal". (2) The spin temperature of CH4 is >
35-38 K, an estimate consistent with the more robust spin temperature found for
H2O. (3) We obtained a 3s upper limit of CH3D/CH4 < 0.020 (D/H < 0.005). This
limit suggests that methane released from the nucleus of C/2004 Q2 is not
dominated by a component formed in extremely cold (near 10 K) environments.
Formation pathways of both interstellar and nebular origin consistent with the
measured D/H in methane are discussed. Evaluating the relative contributions of
these pathways requires further modeling of chemistry including both gas-phase
and gas-grain processes in the natal interstellar cloud and in the
protoplanetary disk.Comment: Accepted by The Astrophysical Journa
The Peculiar Volatile Composition of Comet 8P/Tuttle: A Contact Binary of Chemically Distinct Cometesimals?
We report measurements of eight native (i.e., released directly from the
comet nucleus) volatiles (H2O, HCN, CH4, C2H2, C2H6, CO, H2CO, and CH3OH) in
comet 8P/Tuttle using NIRSPEC at Keck 2. Comet Tuttle reveals a truly unusual
composition, distinct from that of any comet observed to date at infrared
wavelengths. The prominent enrichment of methanol relative to water contrasts
the depletions of other molecules, especially C2H2 and HCN. We suggest that the
nucleus of 8P/Tuttle may contain two cometesimals characterized by distinct
volatile composition. The relative abundances C2/CN, C2/OH, and CN/OH in
8P/Tuttle (measured at optical/near-UV wavelengths) differ substantially from
the mixing ratios of their potential parents (C2H2/HCN, C2H2/H2O, and HCN/H2O)
found in this work. Based on this comparison, our results do not support C2H2
and HCN being the principal precursors for respectively C2 and CN in Tuttle.
The peculiar native composition observed in 8P/Tuttle (compared to other
comets) provides new strong evidence for chemical diversity in the volatile
materials stored in comet nuclei. We discuss the implications of this diversity
for expected variations in the deuterium enrichment of water among comets.Comment: Accepted for Astrophysical Journal Letter
The Unexpectedly Bright Comet C-2012 F6 (Lemmon) Unveiled at Near-Infrared Wavelengths
We acquired near-infrared spectra of the Oort cloud comet C/2012 F6 (Lemmon) at three different heliocentric distances (R h) during the comet's 2013 perihelion passage, providing a comprehensive measure of the outgassing behavior of parent volatiles and cosmogonic indicators. Our observations were performed pre-perihelion at R h = 1.2 AU with CRIRES (on 2013 February 2 and 4), and post-perihelion at R h = 0.75 AU with CSHELL (on March 31 and April 1) and R h = 1.74 AU with NIRSPEC (on June 20). We detected 10 volatile species (H2O, OH* prompt emission, C2H6, CH3OH, H2CO, HCN, CO, CH4, NH3, and NH2), and obtained upper limits for two others (C2H2 and HDO). One-dimensional spatial profiles displayed different distributions for some volatiles, confirming either the existence of polar and apolar ices, or of chemically distinct active vents in the nucleus. The ortho-para ratio for water was 3.31 +/- 0.33 (weighted mean of CRIRES and NIRSPEC results), implying a spin temperature >37 K at the 95% confidence limit. Our (3) upper limit for HDO corresponds to D/H < 2.45 10-3 (i.e., <16 Vienna Standard Mean Ocean Water, VSMOW). At R h = 1.2 AU (CRIRES), the production rate for water was Q(H2O) = 1.9 +/- 0.1 1029 s-1 and its rotational temperature was T rot ~ 69 K. At R h = 0.75 AU (CSHELL), we measured Q(H2O) = 4.6 +/- 0.6 1029 s-1 and T rot = 80 K on March 31, and 6.6 +/- 0.9 1029 s-1 and T rot = 100 K on April 1. At R h = 1.74 AU (NIRSPEC), we obtained Q(H2O) = 1.1 +/- 0.1 1029 s-1 and T rot ~ 50 K. The measured volatile abundance ratios classify comet C/2012 F6 as rather depleted in C2H6 and CH3OH, while HCN, CH4, and CO displayed abundances close to their median values found among comets. H2CO was the only volatile showing a relative enhancement. The relative paucity of C2H6 and CH3OH (with respect to H2O) suggests formation within warm regions of the nebula. However, the normal abundance of HCN and hypervolatiles CH4 and CO, and the enhancement of H2CO, may indicate a possible heterogeneous nucleus of comet C/2012 F6 (Lemmon), possibly as a result of radial mixing within the protoplanetary dis
Parent Volatiles in Comet 9P/Tempel 1: Before and After Impact
We quantified eight parent volatiles (H_2O, C_2H_6, HCN, CO, CH_3OH, H_2CO, C_2H_2, and CH_4) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk
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