Claire Chandler - Academia.edu (original) (raw)
Uploads
Papers by Claire Chandler
The Astrophysical Journal, Aug 20, 1995
The Astrophysical Journal, 1995
The Astrophysical Journal, 1995
We propose to use the Keck Interferometer to investigate the origin of CO bandhead emission from ... more We propose to use the Keck Interferometer to investigate the origin of CO bandhead emission from DG Tau. The CO emission traces the hot (~3000 K), dense (n ⪆ 10^10 cm^-3), neutral material in the inner regions of circumstellar accretion disks, and as such potentially provides important information about the physical, chemical, and dynamical state of the gas in the region where jet production and accretion take place during the formation of solar-type stars. Here we propose to determine whether the CO emission originates inside the dust destruction radius in the disk, or from a more extended, externally- heated surface layer in the disk photosphere, by comparing the visibility of the 2 (micron) continuum with the visibility of a pixel containing the CO emission.
The Astrophysical Journal, 2016
<p>Detection of hot corinos in Solar-like protostars has been so far mostly limited... more <p>Detection of hot corinos in Solar-like protostars has been so far mostly limited to Class 0 objects, hampering our understanding of their origin and evolution. Recent evidence suggests that planet formation probably starts already in Class I protostars, representing a key step in our understanding of their chemical composition at the planet formation scale. Therefore, understanding the fate of hot corinos in Class I protostars has become of paramount importance. In this context, we report the discovery of a hot corino at the heart of the prototypical Class I source L1551 IRS5, obtained via ALMA observations as part of the Large Program FAUST (Fifty AU Study of the chemistry in the disk/envelope system of Solar-like protostars). More specifically, FAUST is the first ALMA Large Program based on astrochemistry and is designed to survey the chemical composition of a sample of 13 Class 0 and I protostars at the planet-formation scale.</p> <p>We detected in L1551 IRS 5 several emission lines from interstellar complex organic molecules (iCOMs) such as methanol and its most abundant isotopologues, as well as methyl formate and ethanol. &#160;The line emission is bright toward the north component (N), although a hot corino in the south component, cannot be excluded. The non-LTE analysis of the methanol lines towards N provides constraints on the gas temperature (~ 100 K), density (&#8805; 1.5 x 10<sup>8</sup> cm<sup>-3</sup>) and emitting size (~0.15&#8221;, i.e. ~ 10 au in radius). The lines are predicted to be optically thick, the <sup>13</sup>CH<sub>3</sub>OH line having an opacity &#8805; 2. The methyl formate and ethanol column densities relative to methanol are &#8804; 0.03 and &#8804; 0.015, respectively, compatible with those measured in Class 0 sources. Thus, the present observations towards L1551 IRS5 agree with little chemical evolution in hot corinos from Class 0 to I.</p> <p>&#160;</p>
The Astrophysical Journal
After almost 20 years of hunting, only about a dozen hot corinos, hot regions enriched in interst... more After almost 20 years of hunting, only about a dozen hot corinos, hot regions enriched in interstellar complex organic molecules (iCOMs), are known. Of them, many are binary systems with the two components showing drastically different molecular spectra. Two obvious questions arise. Why are hot corinos so difficult to find and why do their binary components seem chemically different? The answer to both questions could be a high dust opacity that would hide the molecular lines. To test this hypothesis, we observed methanol lines at centimeter wavelengths, where dust opacity is negligible, using the Very Large Array interferometer. We targeted the NGC 1333 IRAS 4A binary system, for which one of the two components, 4A1, has a spectrum deprived of iCOMs lines when observed at millimeter wavelengths, while the other component, 4A2, is very rich in iCOMs. We found that centimeter methanol lines are similarly bright toward 4A1 and 4A2. Their non-LTE analysis indicates gas density and temperature (≥ 2 × 10 6 cm −3 and 100-190 K), methanol column density (∼ 10 19 cm −2) and extent (∼35 au in radius) similar in 4A1 and 4A2, proving that both are hot corinos. Furthermore, the comparison with previous methanol line millimeter observations allows us to estimate the optical depth of the dust in front of 4A1 and 4A2, respectively. The obtained values explain the absence of iCOMs line emission toward 4A1 at millimeter wavelengths and indicate that the abundances toward 4A2 are underestimated by ∼30%. Therefore, centimeter observations are crucial for the correct study of hot corinos, their census, and their molecular abundances.
The Astrophysical Journal
The Astrophysical Journal
The Astrophysical Journal
Symposium - International Astronomical Union
High-mass star formation is not well understood chiefly because examples are deeply embedded, rel... more High-mass star formation is not well understood chiefly because examples are deeply embedded, relatively distant, and crowded with sources of emission. Using VLA and VLBA observations of H2O and SiO maser emission, we have mapped in detail the structure and proper motion of material 20-500 AU from the closest high-mass YSO, radio source I in the Orion KL region. We observe streams of material driven in a rotating, wide angle, bipolar wind from the the surface of an edge-on accretion disk. The example of source I provides strong evidence that high-mass star formation proceeds via accretion.
The Astrophysical Journal
The Astrophysical Journal Supplement Series
The Astrophysical Journal
Monthly Notices of the Royal Astronomical Society
Monthly Notices of the Royal Astronomical Society
The Astrophysical Journal
Science (New York, N.Y.), Sep 30, 2016
Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks o... more Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array, we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk.
Observatory Operations: Strategies, Processes, and Systems VI, 2016
The Astrophysical Journal, Aug 20, 1995
The Astrophysical Journal, 1995
The Astrophysical Journal, 1995
We propose to use the Keck Interferometer to investigate the origin of CO bandhead emission from ... more We propose to use the Keck Interferometer to investigate the origin of CO bandhead emission from DG Tau. The CO emission traces the hot (~3000 K), dense (n ⪆ 10^10 cm^-3), neutral material in the inner regions of circumstellar accretion disks, and as such potentially provides important information about the physical, chemical, and dynamical state of the gas in the region where jet production and accretion take place during the formation of solar-type stars. Here we propose to determine whether the CO emission originates inside the dust destruction radius in the disk, or from a more extended, externally- heated surface layer in the disk photosphere, by comparing the visibility of the 2 (micron) continuum with the visibility of a pixel containing the CO emission.
The Astrophysical Journal, 2016
<p>Detection of hot corinos in Solar-like protostars has been so far mostly limited... more <p>Detection of hot corinos in Solar-like protostars has been so far mostly limited to Class 0 objects, hampering our understanding of their origin and evolution. Recent evidence suggests that planet formation probably starts already in Class I protostars, representing a key step in our understanding of their chemical composition at the planet formation scale. Therefore, understanding the fate of hot corinos in Class I protostars has become of paramount importance. In this context, we report the discovery of a hot corino at the heart of the prototypical Class I source L1551 IRS5, obtained via ALMA observations as part of the Large Program FAUST (Fifty AU Study of the chemistry in the disk/envelope system of Solar-like protostars). More specifically, FAUST is the first ALMA Large Program based on astrochemistry and is designed to survey the chemical composition of a sample of 13 Class 0 and I protostars at the planet-formation scale.</p> <p>We detected in L1551 IRS 5 several emission lines from interstellar complex organic molecules (iCOMs) such as methanol and its most abundant isotopologues, as well as methyl formate and ethanol. &#160;The line emission is bright toward the north component (N), although a hot corino in the south component, cannot be excluded. The non-LTE analysis of the methanol lines towards N provides constraints on the gas temperature (~ 100 K), density (&#8805; 1.5 x 10<sup>8</sup> cm<sup>-3</sup>) and emitting size (~0.15&#8221;, i.e. ~ 10 au in radius). The lines are predicted to be optically thick, the <sup>13</sup>CH<sub>3</sub>OH line having an opacity &#8805; 2. The methyl formate and ethanol column densities relative to methanol are &#8804; 0.03 and &#8804; 0.015, respectively, compatible with those measured in Class 0 sources. Thus, the present observations towards L1551 IRS5 agree with little chemical evolution in hot corinos from Class 0 to I.</p> <p>&#160;</p>
The Astrophysical Journal
After almost 20 years of hunting, only about a dozen hot corinos, hot regions enriched in interst... more After almost 20 years of hunting, only about a dozen hot corinos, hot regions enriched in interstellar complex organic molecules (iCOMs), are known. Of them, many are binary systems with the two components showing drastically different molecular spectra. Two obvious questions arise. Why are hot corinos so difficult to find and why do their binary components seem chemically different? The answer to both questions could be a high dust opacity that would hide the molecular lines. To test this hypothesis, we observed methanol lines at centimeter wavelengths, where dust opacity is negligible, using the Very Large Array interferometer. We targeted the NGC 1333 IRAS 4A binary system, for which one of the two components, 4A1, has a spectrum deprived of iCOMs lines when observed at millimeter wavelengths, while the other component, 4A2, is very rich in iCOMs. We found that centimeter methanol lines are similarly bright toward 4A1 and 4A2. Their non-LTE analysis indicates gas density and temperature (≥ 2 × 10 6 cm −3 and 100-190 K), methanol column density (∼ 10 19 cm −2) and extent (∼35 au in radius) similar in 4A1 and 4A2, proving that both are hot corinos. Furthermore, the comparison with previous methanol line millimeter observations allows us to estimate the optical depth of the dust in front of 4A1 and 4A2, respectively. The obtained values explain the absence of iCOMs line emission toward 4A1 at millimeter wavelengths and indicate that the abundances toward 4A2 are underestimated by ∼30%. Therefore, centimeter observations are crucial for the correct study of hot corinos, their census, and their molecular abundances.
The Astrophysical Journal
The Astrophysical Journal
The Astrophysical Journal
Symposium - International Astronomical Union
High-mass star formation is not well understood chiefly because examples are deeply embedded, rel... more High-mass star formation is not well understood chiefly because examples are deeply embedded, relatively distant, and crowded with sources of emission. Using VLA and VLBA observations of H2O and SiO maser emission, we have mapped in detail the structure and proper motion of material 20-500 AU from the closest high-mass YSO, radio source I in the Orion KL region. We observe streams of material driven in a rotating, wide angle, bipolar wind from the the surface of an edge-on accretion disk. The example of source I provides strong evidence that high-mass star formation proceeds via accretion.
The Astrophysical Journal
The Astrophysical Journal Supplement Series
The Astrophysical Journal
Monthly Notices of the Royal Astronomical Society
Monthly Notices of the Royal Astronomical Society
The Astrophysical Journal
Science (New York, N.Y.), Sep 30, 2016
Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks o... more Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array, we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk.
Observatory Operations: Strategies, Processes, and Systems VI, 2016