The First Detection of CH2CN in a Protoplanetary Disk

Abstract We report the first detection of the molecule cyanomethyl, CH2CN, in a protoplanetary disk. Until now, CH2CN had only been observed at earlier evolutionary stages, in the molecular clouds TMC-1, Sgr2, and L483, in the prestellar core L1544, and toward the protostar L1527. We detect six transitions of ortho-CH2CN toward the disk around nearby T Tauri star TW Hya. An excitation analysis reveals that the disk-averaged column density, N , for ortho-CH2CN is (6.3 ± 0.5) × 1012 cm−2, which is rescaled to reflect a 3:1 ortho-para ratio, resulting in a total column density, N tot, of (8.4 ± 0.7) × 1012 cm−2. We calculate a disk-average rotational temperature, T rot = 40 ± 5 K, while a radially resolved analysis shows that T rot remains relatively constant across the radius of the disk. This high rotation temperature suggests that in a static disk and if vertical mixing can be neglected, CH2CN is largely formed through gas-phase reactions in the upper layers of the disk, rather than solid-state reactions on the surface of grains in the disk midplane. The integrated intensity radial profiles show a ring structure consistent with molecules such as CN and DCN. We note that this is also consistent with previous lower-resolution observations of centrally peaked CH3CN emission toward the TW Hya disks, since the observed emission gap disappears when convolving our observations with a larger beam size. We obtain a CH2CN/CH3CN ratio ranging between 4 and 10. This high CH2CN/CH3CN is reproduced in a representative chemical model of the TW Hya disk that employs standard static disk chemistry model assumptions, i.e., without any additional tuning.

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Upper limits on CH3OH in the HD 163296 protoplanetary disk

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834353 ◽

2019 ◽

Vol 623 ◽

pp. A124 ◽

Cited By ~ 12

Author(s):

M. T. Carney ◽

M. R. Hogerheijde ◽

V. V. Guzmán ◽

C. Walsh ◽

K. I. Öberg ◽

...

Keyword(s):

Gas Phase ◽

Column Density ◽

Matched Filter ◽

Image Plane ◽

Protoplanetary Disk ◽

Chemical Complexity ◽

Disk Structure ◽

T Tauri ◽

Upper Limits ◽

Integrated Intensity

Context. Methanol (CH3OH) is at the root of organic ice chemistry in protoplanetary disks. Its connection to prebiotic chemistry and its role in the chemical environment of the disk midplane make it an important target for disk chemistry studies. However, its weak emission has made detections difficult. To date, gas-phase CH3OH is detected in only one Class II disk, TW Hya. Aims. We aim to constrain the methanol content of the HD 163296 protoplanetary disk. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to search for a total of four CH3OH emission lines in bands six and seven toward the disk around the young Herbig Ae star HD 163296. The disk-averaged column density of methanol and its related species formaldehyde (H2CO) were estimated assuming optically thin emission in local thermodynamic equilibrium. We compared these results to the gas-phase column densities of the TW Hya disk. Results. No targeted methanol lines were detected with Keplerian masking in the image plane nor with matched filter analysis in the uv plane individually nor after line stacking. The 3σ disk-integrated intensity upper limits are <51 mJy km s−1 for the band six lines and <26 mJy km s−1 for the band seven lines. The band seven lines provide the strictest 3σ upper limit on disk-averaged column density with Navg < 5.0 × 1011 cm−2. The methanol-to-formaldehyde ratio is CH3OH∕H2CO<0.24 in the HD 163296 disk compared to a ratio of 1.27 in the TW Hya disk. Conclusions. The HD 163296 protoplanetary disk is less abundant in methanol with respect to formaldehyde compared to the disk around TW Hya. Differences in the stellar irradiation in this Herbig Ae disk as compared to that of a disk around a T Tauri star likely influence the gaseous methanol and formaldehyde content. Possible reasons for the lower HD 163296 methanol-to-formaldehyde ratio include: a higher than expected gas-phase formation of H2CO in the HD 163296 disk, uncertainties in the grain surface formation efficiency of CH3OH and H2CO, and differences in the disk structure and/or CH3OH and H2CO desorption processes that drive the release of the molecules from ice mantles back into the gas phase. These results provide observational evidence that the gas-phase chemical complexity found in disks may be strongly influenced by the spectral type of the host star.

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Discovery of allenyl acetylene, H2CCCHCCH, in TMC-1

Astronomy and Astrophysics ◽

10.1051/0004-6361/202140482 ◽

2021 ◽

Vol 647 ◽

pp. L3 ◽

Cited By ~ 1

Author(s):

J. Cernicharo ◽

C. Cabezas ◽

M. Agúndez ◽

B. Tercero ◽

N. Marcelino ◽

...

Keyword(s):

Column Density ◽

State Of The Art ◽

Rotational Temperature ◽

Signal To Noise Ratio ◽

Laboratory Data ◽

The Other ◽

Signal To Noise ◽

Chemical Models ◽

Upper Limit

We present the discovery in TMC-1 of allenyl acetylene, H2CCCHCCH, through the observation of nineteen lines with a signal-to-noise ratio ∼4–15. For this species, we derived a rotational temperature of 7 ± 1 K and a column density of 1.2 ± 0.2 × 1013 cm−2. The other well known isomer of this molecule, methyl diacetylene (CH3C4H), has also been observed and we derived a similar rotational temperature, Tr = 7.0 ± 0.3 K, and a column density for its two states (A and E) of 6.5 ± 0.3 × 1012 cm−2. Hence, allenyl acetylene and methyl diacetylene have a similar abundance. Remarkably, their abundances are close to that of vinyl acetylene (CH2CHCCH). We also searched for the other isomer of C5H4, HCCCH2CCH (1.4-Pentadiyne), but only a 3σ upper limit of 2.5 × 1012 cm−2 to the column density can be established. These results have been compared to state-of-the-art chemical models for TMC-1, indicating the important role of these hydrocarbons in its chemistry. The rotational parameters of allenyl acetylene have been improved by fitting the existing laboratory data together with the frequencies of the transitions observed in TMC-1.

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Rotational Fine Structure Lines of Interstellar C2 Toward ζ Persei

Symposium - International Astronomical Union ◽

10.1017/s007418090007265x ◽

1980 ◽

Vol 87 ◽

pp. 263-267

Author(s):

Frederic H. Chaffee ◽

Barry L. Lutz ◽

John H. Black ◽

Paul A. Vanden Bout ◽

Ronald L. Snell

Keyword(s):

Fine Structure ◽

Thermal Equilibrium ◽

Column Density ◽

Rotational Temperature ◽

Detailed Model ◽

Data Yield ◽

Fine Structure Lines

We have detected 9 of the rotational fine structure lines of the 2-0 Phillips band of interstellar C2 toward ζ Persei using the Tull spectrograph and Reticon detector on the 2.7 m telescope at the McDonald Observatory. These data yield a total C2 column density of 1.2 × 1013 cm-2 and a rotational temperature of 97 K compared to 1.4 × 1013 cm-2 and 45 K predicted by the detailed model of the cloud by Black, Hartquist and Dalgarno. We suggest that radiative pumping through the Mulliken and Phillips systems has modified the C2 level populations in such a way as to produce an observed rotational temperature which exceeds that arising in pure thermal equilibrium.

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Mottled Protoplanetary Disk Ionization by Magnetically Channeled T Tauri Star Energetic Particles

The Astrophysical Journal ◽

10.3847/1538-4357/aaa48b ◽

2018 ◽

Vol 853 (2) ◽

pp. 112 ◽

Cited By ~ 10

Author(s):

F. Fraschetti ◽

J. J. Drake ◽

O. Cohen ◽

C. Garraffo

Keyword(s):

Energetic Particles ◽

Protoplanetary Disk ◽

Tauri Star ◽

T Tauri

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Investigation of chemical differentiation among the NGC 2264 cluster-forming clumps

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa012 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2395-2409 ◽

Cited By ~ 1

Author(s):

Kotomi Taniguchi ◽

Adele Plunkett ◽

Eric Herbst ◽

Kazuhito Dobashi ◽

Tomomi Shimoikura ◽

...

Keyword(s):

Column Density ◽

Point Sources ◽

Emission Lines ◽

Filamentary Structure ◽

Molecular Emission ◽

Sky Survey ◽

Integrated Intensity ◽

Positive Correlations ◽

Density Ratios ◽

Massive Cluster

ABSTRACT We have carried out mapping observations of molecular emission lines of HC3N and CH3OH toward two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, using the Nobeyama 45-m radio telescope. We derive an I(HC3N)/I(CH3OH) integrated intensity ratio map, showing a higher value at clumps including 2MASS (Two Micron All Sky Survey) point sources at the northern part of NGC 2264-D. Possible interpretations of the I(HC3N)/I(CH3OH) ratio are discussed. We have also observed molecular emission lines from CCS and N2H+ toward five positions in each clump. We investigate the N(N2H+)/N(CCS) and N(N2H+)/N(HC3N) column density ratios among the ten positions in order to test whether they can be used as chemical evolutionary indicators in these clumps. The N(N2H+)/N(CCS) ratio shows a very high value toward a bright embedded IR source (IRS1), whereas the N(N2H+)/N(HC3N) ratio at IRS1 is comparable with those at the other positions. These results suggest that ultraviolet radiation affects the chemistry around IRS1. We find that there are positive correlations between these column density ratios and the excitation temperatures of N2H+, which implies the chemical evolution of clumps. These chemical evolutionary indicators likely reflect the combination of evolution along the filamentary structure and evolution of each clump.

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An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS in a protoplanetary disk

Astronomy and Astrophysics ◽

10.1051/0004-6361/202141881 ◽

2021 ◽

Vol 653 ◽

pp. L5

Author(s):

N. T. Phuong ◽

A. Dutrey ◽

E. Chapillon ◽

S. Guilloteau ◽

J. Bary ◽

...

Keyword(s):

Protoplanetary Disk ◽

Vertical Temperature ◽

Physical Conditions ◽

Outer Disk ◽

T Tauri ◽

Disk Size ◽

Chemical Content ◽

Complex Chemical Composition ◽

Good Laboratory ◽

Low Temperature Chemistry

Context. Molecular line surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs), the birthplace of planets. The large radial and vertical temperature as well as density gradients in these PPDs lead to a complex chemical composition, making chemistry an important step to understand the variety of planetary systems. Aims. We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T Tauri system. Methods. We used NOEMA with the new correlator PolyFix to observe rotational lines at ∼2.6 to 4 mm from a few dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance relative to 13CO, which we compare to those of the TMC1 cloud and LkCa 15 disk. Results. We report the first detection of CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of them had been found previously, while seven others (13CN, N2H+, HNC, DNC, HC3N, CCS, and C34S) are new detections in this disk. Conclusions. The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived from DCO+/HCO+, DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detection of the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks to its large disk size and mass.

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Organic molecules in the protoplanetary disk of DG Tauri revealed by ALMA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834475 ◽

2019 ◽

Vol 623 ◽

pp. L6 ◽

Cited By ~ 13

Author(s):

L. Podio ◽

F. Bacciotti ◽

D. Fedele ◽

C. Favre ◽

C. Codella ◽

...

Keyword(s):

Column Density ◽

Protoplanetary Disks ◽

Temperature Inversion ◽

Abundance Ratio ◽

Chemical Compositions ◽

Outer Disk ◽

T Tauri ◽

Dust Distribution ◽

Disk Height ◽

Co Emission

Context. Planets form in protoplanetary disks and inherit their chemical compositions. Aims. It is thus crucial to map the distribution and investigate the formation of simple organics, such as formaldehyde and methanol, in protoplanetary disks. Methods. We analyze ALMA observations of the nearby disk-jet system around the T Tauri star DG Tau in the o − H2CO 31, 2 − 21, 1 and CH3OH 3−2, 2 − 4−1, 4 E, 50, 5 − 40, 4 A transitions at an unprecedented resolution of $ {\sim}0{{\overset{\prime\prime}{.}}}{15} $, i.e., ∼18 au at a distance of 121 pc. Results. The H2CO emission originates from a rotating ring extending from ∼40 au with a peak at ∼62 au, i.e., at the edge of the 1.3 mm dust continuum. CH3OH emission is not detected down to an rms of 3 mJy beam−1 in the 0.162 km s−1 channel. Assuming an ortho-to-para ratio of 1.8−2.8 the ring- and disk-height-averaged H2CO column density is ∼0.3−4 × 1014 cm−2, while that of CH3OH is < 0.04−0.7 × 1014 cm−2. In the inner 40 au no o − H2CO emission is detected with an upper limit on its beam-averaged column density of ∼0.5−6 × 1013 cm−2. Conclusions. The H2CO ring in the disk of DG Tau is located beyond the CO iceline (RCO ∼ 30 au). This suggests that the H2CO abundance is enhanced in the outer disk due to formation on grain surfaces by the hydrogenation of CO ice. The emission peak at the edge of the mm dust continuum may be due to enhanced desorption of H2CO in the gas phase caused by increased UV penetration and/or temperature inversion. The CH3OH/H2CO abundance ratio is < 1, in agreement with disk chemistry models. The inner edge of the H2CO ring coincides with the radius where the polarization of the dust continuum changes orientation, hinting at a tight link between the H2CO chemistry and the dust properties in the outer disk and at the possible presence of substructures in the dust distribution.

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Detection of New Ammonia Sources

Symposium - International Astronomical Union ◽

10.1017/s0074180900072211 ◽

1980 ◽

Vol 87 ◽

pp. 83-84

Author(s):

G.H. Macdonald ◽

A.T. Brown ◽

L.T. Little ◽

D.N. Matheson ◽

M. Felli

Keyword(s):

Hyperfine Structure ◽

Molecular Hydrogen ◽

Molecular Clouds ◽

Column Density ◽

Rotational Temperature ◽

Kinetic Temperature ◽

Excitation Temperature ◽

Hydrogen Density

Ammonia is a favoured molecule for the study of molecular clouds since several important parameters of the cloud can be deduced from simple observations of the J,K=1,1 and 2,2 inversion doublet transitions and the hyperfine structure in the (1,1) line. With the additional knowledge of the kinetic temperature Tk from observations of CO, for example, it is possible to compute the excitation temperature of the (1,1) line (T11), the rotational temperature between the (1,1) and (2,2) levels (T21), the molecular hydrogen density n(H2) and ammonia column density N(NH3) (see, for example, Martin and Barrett, 1978).

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HI in the outskirts of Nearby Spirals

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316011303 ◽

2016 ◽

Vol 11 (S321) ◽

pp. 235-237

Author(s):

Elias Brinks ◽

António Portas

Keyword(s):

Spiral Galaxy ◽

Surface Density ◽

Column Density ◽

Large Radius ◽

Type Function ◽

Radial Profiles ◽

Atomic Gas ◽

Turn Over

AbstractWe analyse nine galaxies taken from the THINGS survey to investigate the H I extent of spiral galaxy disks. We exploit the high spatial and velocity resolution, and the sensitivity of THINGS to investigate where the atomic gas disks end and what might shape their outskirts. We find that the atomic gas surface density across most of the disk is constant at 5 to 10 M⊙ pc−2 and declines at large radius. The shape of the H I distribution can be described by a Sérsic–type function with a slope index n = 0.18 – 0.36. The H I column density at which radial profiles turn over is found to be at too high a level for it to be caused by ionisation by a meta–galactic UV field. Instead we suggest the H I extent is rather set by how galaxy disks form.

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