1,123 research outputs found
Comparison of 30 THz impulsive burst time development to microwaves, H-alpha, EUV, and GOES soft X-rays
The recent discovery of impulsive solar burst emission in the 30 THz band is
raising new interpretation challenges. One event associated with a GOES M2
class flare has been observed simultaneously in microwaves, H-alpha, EUV, and
soft X-ray bands. Although these new observations confirm some features found
in the two prior known events, they exhibit time profile structure
discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the
Neupert effect). These results suggest a more complex relationship between 30
THz emission and radiation produced at other wavelength ranges. The multiple
frequency emissions in the impulsive phase are likely to be produced at a
common flaring site lower in the chromosphere. The 30 THz burst emission may be
either part of a nonthermal radiation mechanism or due to the rapid thermal
response to a beam of high-energy particles bombarding the dense solar
atmosphere.Comment: accepted to Astronomy and Astrophysic
A new protonated molecule discovered in TMC-1: HCCNCH+
In recent years we have seen an important increase in the number of
protonated molecules detected in cold dense clouds. Here we report the
detection in TMC-1 of HCCNCH+, the protonated form of HCCNC, which is a
metastable isomer of HC3N. This is the first protonated form of a metastable
isomer detected in a cold dense cloud. The detection was based on observations
carried out with the Yebes 40m and IRAM 30m telescopes, which revealed four
harmonically related lines. We derive a rotational constant B = 4664.431891 +/-
0.000692 MHz and a centrifugal distortion constant D = 519.14 +/- 4.14 Hz. From
a high-level ab initio screening of potential carriers we confidently assign
the series of lines to the ion HCCNCH+. We derive a column density of (3.0 +/-
0.5)e10 cm-2 for HCCNCH+, which results in a HCCNCH+/HCCNC abundance ratio of
0.010 +/- 0.002. This value is well reproduced by a state-of-the-art chemical
model, which however is subject to important uncertainties regarding the
chemistry of HCCNCH+. The observational and theoretical status of protonated
molecules in cold dense clouds indicate that there exists a global trend in
which protonated-to-neutral abundance ratios MH+/M increase with increasing
proton affinity of the neutral M, although if one restricts to species M with
high proton affinities (>700 kJ/mol), MH+/M ratios fall in the range 0.001-0.1,
with no apparent correlation with proton affinity. We suggest various
protonated molecules that are good candidates for detection in cold dense
clouds in the near future.Comment: Accepted for publication in A&A Letter
Discovery of interstellar NC4NH+: dicyanopolyynes are indeed abundant in space
The previous detection of two species related to the non polar molecule
cyanogen (NCCN), its protonated form (NCCNH+) and one metastable isomer (CNCN),
in cold dense clouds supported the hypothesis that dicyanopolyynes are abundant
in space. Here we report the first identification in space of NC4NH+, which is
the protonated form of NC4N, the second member of the series of dicyanopolyynes
after NCCN. The detection was based on the observation of six harmonically
related lines within the Yebes 40m line survey of TMC-1 QUIJOTE. The six lines
can be fitted to a rotational constant B = 1293.90840 +/- 0.00060 MHz and a
centrifugal distortion constant D = 28.59 +/- 1.21 Hz. We confidently assign
this series of lines to NC4NH+ based on high-level ab initio calculations,
which supports the previous identification of HC5NH+ by Marcelino et al. (2020)
from the observation of a series of lines with a rotational constant 2 MHz
lower than that derived here. The column density of NC4NH+ in TMC-1 is (1.1
+1.4 -0.6)e10 cm-2, which implies that NC4NH+ is eight times less abundant than
NCCNH+. The species CNCN, previously reported toward L483 and tentatively in
TMC-1, is confirmed in this latter source. We estimate that NCCN and NC4N are
present in TMC-1 with abundances a few times to one order of magnitude lower
than HC3N and HC5N, respectively. This means that dicyanopolyynes NC-(CC)n-CN
are present at a lower level than the corresponding monocyanopolyynes
HCC-(CC)n-CN. The reactions of the radicals CN and C3N with HNC arise as the
most likely formation pathways to NCCN and NC4N in cold dense clouds.Comment: Accepted for publication in A&A Letter
Discovery of the propargyl radical (CH2CCH) in TMC-1: one of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds
We present the first identification in interstellar space of the propargyl
radical (CH2CCH). This species was observed in the cold dark cloud TMC-1 using
the Yebes 40m telescope. The six strongest hyperfine components of the
2,0,2-1,0,1 rotational transition, lying at 37.46~GHz, were detected with
signal-to-noise ratios in the range 4.6-12.3 sigma. We derive a column density
of 8.7e13 cm-2 for CH2CCH, which translates to a fractional abundance relative
to H2 of 8.7e-9. This radical has a similar abundance to methyl acetylene, with
an abundance ratio CH2CCH/CH3CCH close to one. The propargyl radical is thus
one of the most abundant radicals detected in TMC-1, and it is probably the
most abundant organic radical with a certain chemical complexity ever found in
a cold dark cloud. We constructed a gas-phase chemical model and find
calculated abundances that agree with, or fall two orders of magnitude below,
the observed value depending on the poorly constrained low-temperature
reactivity of CH2CCH with neutral atoms. According to the chemical model, the
propargyl radical is essentially formed by the C + C2H4 reaction and by the
dissociative recombination of C3Hn+ ions with n = 4-6. The propargyl radical is
believed to control the synthesis of the first aromatic ring in combustion
processes, and it probably plays a key role in the synthesis of large organic
molecules and cyclization processes to benzene in cold dark clouds.Comment: Accepted for publication in A&A Letter
Discovery of HC4NC in TMC-1: A study of the isomers of HC3N, HC5N, and HC7N
We present a study of the isocyano isomers of the cyanopolyynes HC3N, HC5N,
and HC7N in TMC-1 and IRC+10216 carried out with the Yebes 40m radio telescope.
This study has enabled us to report the detection, for the first time in space,
of HCCCCNC in TMC-1 and to give upper limits for HC6NC in the same source. In
addition, the deuterated isotopologues of HCCNC and HNCCC were detected, along
with all 13C substitutions of HCCNC, also for the first time in space. The
abundance ratios of HC3N and HC5N, with their isomers, are very different in
TMC-1 and IRC+10216, namely, N(HC5N)/N(HC4NC) is 300 and >2100, respectively.
We discuss the chemistry of the metastable isomers of cyanopolyynes in terms of
the most likely formation pathways and by comparing observational abundance
ratios between different sources.Comment: This article was submitted to A&A on 27/08/2020 and accepted for
publication on 11/09/202
Discovery of two metallic cyanoacetylides in IRC+10216: HMgCCCN and NaCCCN
We report on the detection of a series of six lines in the ultra-deep Q-band
integration toward IRC+10216 carried out with the Yebes 40m telescope, which
are in harmonic relation with integer quantum numbers J from 12 to 18. After a
detailed analysis of all possible carriers, guided by high-level quantum
chemical calculations, we conclude that the lines belong to HMgCCCN, named
hydromagnesium cyanoacetylide. The rotational temperature and column density
derived for HMgCCCN are 17.1 +/- 2.8K and (3.0 +/- 0.6) e12 cm-2, respectively.
The observed abundance ratio between MgCCCN and HMgCCCN is 3. In addition, we
report the discovery in space, also toward IRC+10216, of sodium cyanoacetylide,
NaCCCN, for which accurate laboratory data are available. For this species we
derive a rotational temperature of 13.5 +/- 1.7K and a column density of (1.2
+/- 0.2) e11 cm-2.Comment: Accepted in Astronomy & Astrophysics as Letter to the Editor on April
3rd, 202
Discovery of HC3O+ in space: The chemistry of O-bearing species in TMC-1
Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of
harmonically related lines with a rotational constant B0=4460.590 +/- 0.001 MHz
and a distortion constant D0=0.511 +/- 0.005 kHz towards the cold dense core
TMC-1. High-level-of-theory ab initio calculations indicate that the best
possible candidate is protonated tricarbon monoxide, HC3O+. We have succeeded
in producing this species in the laboratory and observed its J = 2-1 and 3-2
rotational transitions. Hence, we report the discovery of HC3O+ in space based
on our observations, theoretical calculations, and laboratory experiments. We
derive an abundance ratio N(C3O)/N(HC3O+) = 7. The high abundance of the
protonated form of C3O is due to the high proton affinity of the neutral
species. The chemistry of O-bearing species is modelled, and predictions are
compared to the derived abundances from our data for the most prominent
O-bearing species in TMC-1.Comment: Accepted for publication in A&A Letter
Discovery of the C7N- anion in TMC-1 and IRC+10216
We report on the discovery of the C7N- anion towards the starless core TMC-1
and towards the carbon-rich evolved star IRC+10216. We used the data of the
QUIJOTE line survey towards TMC-1 and found six lines in perfect harmonic
frequency relation from J=27-26 up to J=32-31. The frequency of the lines can
be reproduced with a rotational constant and a distortion constant of
B=582.68490+/-0.00024 MHz and D=4.01+/-0.13 Hz, respectively. The standard
deviation of the fit is 4 kHz. Towards IRC+10216, we identify 17 lines from
J=27-26 up to J=43-42; their frequencies are also in harmonic relation,
providing B=582.6827+/-0.00085 MHz and D=3.31+/-0.31 Hz. The nearly exact
coincidence of the rotational and distortion constants in both sources points
unambiguously to a common molecular carrier. Taking into account the chemical
peculiarities of both sources, the carrier could be a radical or an anion. The
radical can be discarded, as the observed lines belong to a singlet species.
Hence, the most plausible carrier is an anion. High-level ab initio
calculations indicate that C7N-, for which we compute a rotational constant of
B=582.0 MHz and a dipole moment of 7.5 D, is the carrier of the lines in both
sources. We predict the neutral C7N to have a ground electronic state 2Pi and a
dipole moment around 1 D. Because of this low dipole moment value and to its
much larger rotational partition function, its lines are expected to be well
below the sensitivity of our data for both sources.Comment: Accepted as a Letter to the Editor in Astronomy & Astrophysics.
Submitted on 29/12/2022 and accepted on 30/1/202
Interstellar nitrile anions: Detection of C3N- and C5N- in TMC-1
We report on the first detection of C3N- and C5N- towards the cold dark core
TMC-1 in the Taurus region, using the Yebes 40 m telescope. The observed
C3N/C3N- and C5N/C5N- abundance ratios are 140 and 2, respectively; that is
similar to those found in the circumstellar envelope of the carbon-rich star
IRC+10216. Although the formation mechanisms for the neutrals are different in
interstellar (ion-neutral reactions) and circumstellar clouds
(photodissociation and radical-neutral reactions), the similarity of the
C3N/C3N- and C5N/C5N- abundance ratios strongly suggests a common chemical path
for the formation of these anions in interstellar and circumstellar clouds. We
discuss the role of radiative electronic attachment, reactions between N atoms
and carbon chain anions Cn-, and that of H- reactions with HC3N and HC5N as
possible routes to form CnN-. The detection of C5N- in TMC-1 gives strong
support for assigning to this anion the lines found in IRC+10216, as it
excludes the possibility of a metal-bearing species, or a vibrationally excited
state. New sets of rotational parameters have been derived from the observed
frequencies in TMC-1 and IRC+10216 for C5N- and the neutral radical C5N.Comment: Accepted for publication in A&A Letter
Discovery of two new interstellar molecules with QUIJOTE: HCCCHCCC and HCCCCS
We report on the discovery of two new molecules, HCCCHCCC and HCCCCS, towards
the starless core TMC-1 in the Taurus region from the QUIJOTE line survey in
the 31.1-50.2 GHz frequency range. We identify a total of twenty-nine lines of
HCCCHCCC and six rotational transitions of HCCCCS. The rotational quantum
numbers range from Ju=10 up to 15 and Ka <=2 for HCCCHCCC and Ju=21/2 up to
31/2 for HCCCCS. We derived a column density for HCCCHCCC of
N=(1.3+/-0.2)x10^11 cm-2 with a rotational temperature of 6+/-1 K, while for
HCCCCS we derived N=(9.5+/-0.8)x10^10 cm-2 and Trot =10+/-1 K. The abundance of
HCCCHCCC is higher than that of its recently discovered isomer, l-H2C6. If we
compare HCCCCS with its related molecules, HCS and HCCS, we obtain abundance
ratios HCS/HCCCCS=58 and HCCS/HCCCCS=7.2. We investigated the formation of
these two molecules using chemical modelling calculations. The observed
abundances can be accounted for by assuming standard gas-phase formation routes
involving neutral-neutral reactions and ion-neutral reactions.Comment: arXiv admin note: text overlap with arXiv:2206.0899
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