Abstract
A new interstellar molecule, FeC (
X
3
Δ
i
), has been identified in the circumstellar envelope of the carbon-rich asymptotic giant branch star IRC+10216. FeC is the second iron-bearing ...species conclusively observed in the interstellar medium, in addition to FeCN, also found in IRC+10216. The
J
= 4 → 3, 5 → 4, and 6 → 5 rotational transitions of this free radical near 160, 201, and 241 GHz, respectively, were detected in the lowest spin–orbit ladder, Ω = 3, using the Submillimeter Telescope of the Arizona Radio Observatory (ARO) for the 1 mm lines and the ARO 12 m at 2 mm. Because the ground state of FeC is inverted, these transitions are the lowest energy lines. The detected features exhibit slight U shapes with LSR velocities near
V
LSR
≈ −26 km s
−1
and linewidths of Δ
V
1/2
≈ 30 km s
−1
, line parameters characteristic of IRC+10216. Radiative transfer modeling of FeC suggests that the molecule has a shell distribution with peak radius near 300
R
*
(∼6″) extending out to ∼500
R
*
(∼10″) and a fractional abundance, relative to H
2
, of
f
∼ 6 × 10
−11
. The previous FeCN spectra were also modeled, yielding an abundance of
f
∼ 8 × 10
−11
in a larger shell situated near 800
R
*
. These distributions suggest that FeC may be the precursor species for FeCN. Unlike cyanides and carbon-chain molecules, diatomic carbides with a metallic element are rare in IRC+10216, with FeC being the first such detection.
PO and PN have been newly identified in several oxygen-rich circumstellar envelopes, using the Submillimeter Telescope of the Arizona Radio Observatory. The J = 5 → 4 and J = 6 → 5 transitions of PN ...near 235 and 282 GHz, and the lambda doublets originating in the J = 5.5 → 4.5 and J = 6.5 → 5.5 lines of PO at 240 and 284 GHz, have been detected toward the shells of asymptotic giant branch (AGB) stars TX Cam and R Cas. A similar set of lines has been observed toward the supergiant NML Cyg, and new transitions of these two molecules were also measured toward the AGB star IK Tau. Along with the previous data from VY Canis Majoris (VY CMa), these spectral lines were analyzed using the non-local thermodynamic equilibrium (non-LTE) circumstellar modeling code, ESCAPADE. For the AGB stars, peak abundances found for PN and PO were f ∼ (1-2) × 10−8 and (0.5-1) × 10−7, respectively, while those for the supergiants were f(PN) ∼ (0.3-0.7) × 10−8 and f(PO) ∼ (5-7) × 10−8. PN was well modeled with a spherical radial distribution, suggesting formation near the stellar photosphere, perhaps enhanced by shocks. PO was best reproduced by a shell model, indicating a photochemical origin, except for VY CMa. Overall, the abundance of PO is a factor of 5-20 greater than that of PN. This study suggests that phosphorus-bearing molecules are common in O-rich envelopes, and that a significant amount of phosphorus (>20%) remains in the gas phase.
Abstract
The PO molecule (
X
2
Π
r
) has been detected toward Orion-KL via its
J
= 2.5 → 1.5 transition near 109 GHz using the 12 m telescope of the Arizona Radio Observatory. This transition ...consists of a quartet of lines, generated by lambda-doubling and phosphorus hyperfine interactions, creating a distinct pattern of doublets of doublets. All four features (
F
= 3 → 2,
e, f
and 2 → 1,
e, f
) were detected. The line profiles measured were relatively broad, with Δ
V
1/2
∼ 21–25 km s
−1
, and
V
LSR
∼ 10 km s
−1
, clearly identifying the molecule as arising from the Orion “plateau” region. The
J
= 2 → 1 transition of PN (
X
1
Σ) at 94 GHz was also measured, and its line profile indicates a plateau origin in Orion, as found previously by Ziurys. Therefore, PO and PN arise from the same gas. There was no evidence of a “hot core” or “ridge” component in either molecule. The column densities determined for PO and PN in the Orion plateau are
N
tot
≈ 5.4(0.2) × 10
13
and 2.0(0.4) × 10
13
cm
−2
, respectively, with corresponding abundances, relative to H
2
, of
f
∼ 1.6(0.1) × 10
−10
and 6.1(0.6) × 10
−11
, resulting in PO/PN ∼ 3. The PO and PN line profiles also resemble those of SiO and SiS, suggesting that the phosphorus molecules are produced by shocks in the plateau outflow. The observed PO/PN ratio in Orion-KL is very close in value to that measured in other warm molecular clouds, indicating a common synthesis pathway for these two molecules in outflows caused by star formation.
Abstract The red hypergiant VY CMa is famous for its very visible record of high-mass-loss events. Recent CO observations with the Atacama Large Millimeter/submillimeter Array (ALMA) revealed three ...previously unknown large-scale outflows (Singh et al). In this paper, we use the CO maps to investigate the motions of a cluster of four clumps close to the star, not visible in the optical or infrared images. We present their proper motions measured from two epochs of ALMA images and determine the line-of-sight velocities of the gas in emission at the clumps. We estimate their masses and ages, or time since ejection, and conclude that all four were ejected during VY CMa’s active period in the early 20th century. Together with two additional knots observed with the Hubble Space Telescope, VY CMa experienced at least six massive outflows during a 30 yr period, with a total mass lost ≥0.07 M ⊙ . The position–velocity map of the 12 CO emission reveals previously unnoticed attributes of the older outer ejecta. In a very narrow range of Doppler velocities, 12 CO absorption and emission causes some of this outer material to be quite opaque. At those frequencies the inner structure is hidden and we see only emission from an extended outer region. This fact produces a conspicuous but illusory dark spot if one attempts to subtract the continuum in a normal way.
Extensive observations of acetamide (CH3CONH2) and formamide (NH2CHO) have been conducted toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope (SMT) and the 12 m antenna of the ...Arizona Radio Observatory. Over the frequency range 65-280 GHz, 132 transitions of acetamide have been observed as individual, distinguishable features, although in some cases they are partially blended. The unblended transitions in acetamide indicate V LSR = 63.2 ? 2.8 km s--1 and Delta *DV 1/2 = 12.5 ? 2.9 km s--1, line parameters that are very similar to that of formamide (NH2CHO) and other organic species in Sgr B2(N). For formamide, 79 individual transitions were identified over the same frequency region. Rotational diagram analyses indicate the presence of two components for both species in Sgr B2(N). For acetamide, the colder component (Eu < 40 K) exhibits a rotational temperature of T rot = 17 ? 4 K and a column density of N tot = 5.2 ? 3.5 X 1013 cm--2; the higher energy component has T rot = 171 ? 4 K and N tot = 6.4 ? 4.7 X 1014 cm--2. In the case of formamide, T rot = 26 ? 4 K and N tot = 1.6 ? 0.7 X 1014 cm--2 for the colder component with T rot = 134 ? 17 K and N tot = 4.0 ? 1.2 X 1014 cm--2 for the warmer region. The fractional abundances of acetamide are f (H2) = 1.7 X 10--11 and 2.1 X 10--10 for the cold and warm components, and in formamide, f (H2) = 5.3 X 10--11 and 1.3 X 10--10. The similarity between the abundances and distributions of CH3CONH2 and NH2CHO suggests a synthetic connection. The abundance of acetamide, moreover, is only a factor of three lower than that of formaldehyde, and very similar to acetaldehyde and ketene. CH3CONH2 is therefore one of the most abundant complex organic species in Sgr B2(N), and could be a possible source of larger peptide molecules, as opposed to amino acids.
The hydrocarbons CCH and c-C3H2 have been detected at multiple positions distributed across the Helix, along with the CN, indicating that these molecules are present throughout this very old ...planetary nebula. The species were identified by observations of the N = 1 → 0 transitions of CCH and CN and the J = 21,2 → 10,1 transition of c-C3H2, conducted with the new Atacama Large Millimeter/submillimeter Array (ALMA) prototype 12 m antenna of the Arizona Radio Observatory at 3 mm in wavelength. Column densities of the three species were calculated to be Ntot(CCH) ∼ (0.8-6.6) × 1012 cm−2, Ntot(c-C3H2) ∼ (0.3-5.9) × 1011 cm−2, and Ntot(CN) ∼ (0.7-7.4) × 1012 cm−2, corresponding to fractional abundances, with respect to H2, of f(CCH) ∼ (1.1-8.8) × 10−7, f(c-C3H2) ∼ (0.4-7.9) × 10−8, and f(CN) ∼ (0.9-9.9) × 10−7. Surprisingly, the abundances are comparable to those measured in younger planetary nebulae (PNe), indicating that predicted photodestruction processes for gas-phase molecules are inefficient in these objects, even over long timescales. The distributions of these two hydrocarbons in the Helix appear to be correlated, with a ratio of CCH/c-C3H2 ∼ 5-80 and an average value of 29 6-remarkably similar to both the range (CCH/c-C3H2 ∼ 11-53) and average value (28.2 1.4) found in diffuse clouds. The abundances of CCH, c-C3H2, and CN in the Helix are also factors of 10-100 greater than those measured in diffuse gas. These results suggest that molecular ejecta from PNe are a possible external source for polyatomic species found in diffuse clouds, including C60.
Abstract
A sensitive (1
σ
rms ≤ 3 mK; 2 MHz resolution) 1 mm spectral survey (214.5–285.5 GHz) of the envelope of the oxygen-rich supergiant star NML Cygni (NML Cyg) has been conducted using the 10 m ...Submillimeter Telescope of the Arizona Radio Observatory. These data represent the first spectral line survey of NML Cyg and are complementary to a previous 1 mm survey of the envelope of a similar hypergiant, VY Canis Majoris (VY CMa). The complete NML Cyg data set is presented here. In the survey, 104 emission lines were observed, arising from 17 different molecules and 4 unidentified features. Many of the observed features have complex line profiles, arising from asymmetric outflows characteristic of hypergiant stars. While most of the lines in the survey arise from SiO, SO, SO
2
, and SiS, CO had the strongest emission. Five other C-bearing species are identified in the survey (HCN, CN, HCO
+
, CS, and HNC), demonstrating an active carbon chemistry despite the O-rich environment. Moreover, NS was observed, but not NO, although favorable transitions of both molecules lie in the surveyed region. Sulfur chemistry appears to be prominent in NML Cyg and plays an important role in the collimated outflows. The refractory species observed, NaCl and AlO, have narrow emission lines, indicating that these molecules do not reach the terminal expansion velocity. NaCl and AlO likely condense into dust grains at r < 50
R
*
. From NaCl, the chlorine isotope ratio was determined to be
35
Cl/
37
Cl = 3.85 ± 0.30.
Abstract
The
J
= 2 → 1 transition of CO near 230 GHz and the
J
= 3 → 2 line of HCN at 265 GHz have been imaged in the envelope of the red hypergiant star, VY Canis Majoris (VY CMa), using the Atacama ...Large Millimeter Array (ALMA) with angular resolutions 0.″2–1.″5; single-dish data were added to provide sensitivity up to 30″. These images reveal a far more complex envelope, with previously unseen outflows extending 4″–9″ from the star. These new structures include an arc-like outflow with an angular separation of ∼9″ northeast from the stellar position (“NE Arc”), twin fingerlike features approximately 4″ to the north/northeast (“NE Extension”), and a roughly spherical region observed ∼7″ E of the star (“E Bubble”). The NE Arc appears to be decelerating from base (
V
LSR
∼ 7 km s
−1
) to tip (
V
LSR
∼ 18 km s
−1
), while the NE Extension is blueshifted with
V
LSR
∼ −7 km s
−1
. Among the new features, HCN is only detected in the NE Arc. In addition, known structures Arc 1, Arc 2, and NW Arc, as well as other features closer to the star, are closely replicated in CO, suggesting that the gas and dust are well mixed. The CO spectra are consistent with the kinematic picture of VY CMa derived from HST data. Arc 2, however, has added complexity. Preliminary results from CO suggest
12
C/
13
C ∼ 22–38 across the envelope. The additional presence of at least three major episodic mass ejection events significantly broadens the current perspective of the envelope structure and mass-loss history of VY CMa.
A new circumstellar molecule, the radical AlO (X 2+), has been detected toward the envelope of the oxygen-rich supergiant star VY Canis Majoris (VY CMa) using the Arizona Radio Observatory (ARO). The ...N = 7 -> 6 and 6 -> 5 rotational transitions of AlO at 268 and 230 GHz were observed at 1 mm using the ARO Submillimeter Telescope (SMT) and the N = 4 -> 3 line was detected at 2 mm using the ARO 12 m telescope. Based on the shape of the line profiles, AlO most likely arises from the dust-forming region in the spherical outflow of VY CMa, as opposed to the blue or redshifted winds, with a source size of c s ~ 05. Given this source size, the column density of AlO was found to be N tot ~ 2 X 1015 cm-2 for T rot ~ 230 K, with a fractional abundance, relative to H2, of ~10-8. Gas-phase thermodynamic equilibrium chemistry is the likely formation mechanism for AlO in VY CMa, but either shocks disrupt the condensation process into Al2O3, or chemical 'freezeout' occurs. The species therefore survives further into the circumstellar envelope to a radius of r ~ 20 R *. The detection of AlO in VY CMa is additional evidence of an active gas-phase refractory chemistry in oxygen-rich envelopes, and suggests such objects may be fruitful sources for other new oxide identifications.
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