52 research outputs found
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 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
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 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
El SIG espacio SiAR, una herramienta del mapa a disposición del regadÃo español para la optimización del uso del agua gracias a las imágenes satélite
Comunicación presentada al XXXVII Congreso Nacional de Riegos, celebrado en Don Benito del 4 al 6 de Junio de 2019 y organizada por la Asociación Española de Riegos y Drenajes y la Universidad de ExtremaduraEl Sistema de Información Agroclimática para el RegadÃo (SiAR), tiene como misión la optimización del uso de agua en el regadÃo, promoviendo su sostenibilidad económica, social y medioambiental, mediante el asesoramiento a los regantes, facilitándoles información agroclimática relevante y estimaciones de riego. La Subdirección General de RegadÃos e Infraestructuras Rurales ha desarrollado el proyecto ESPACIO SiAR, una herramienta webSIG que se integra los datos procedentes de las estaciones SiAR, ubicadas
en las principales zonas regables, con las secuencias temporales de los satélites Landsat 8 y Sentinel 2A y 2B. Su objetivo principal es el de realizar un seguimiento mediante teledetección de los cultivos que permita determinar con la mayor precisión posible las necesidades hÃdricas de los cultivos, para emplear el agua necesaria en el momento preciso. La información obtenida se pone a disposición de forma gratuita y abierta, mediante el visor ESPACIO SiAR en la página web www.espaciosiar.es, para un amplio abanico de usuarios potenciales, como son los regantes individuales, gestores de comunidades de regantes, servicios de asesoramiento y la propia administración para la planificación de los recursos hÃdricos a corto, medio y largo plazo
Detection of ethanol, acetone, and propanal in TMC-1: New O-bearing complex organics in cold sources
We present the detection of ethanol (C2H5OH), acetone (CH3COCH3), and
propanal (C2H5CHO) toward the cyanopolyyne peak of TMC-1. These three O-bearing
complex organic molecules are known to be present in warm interstellar clouds,
but had never been observed in a starless core. The addition of these three new
pieces to the puzzle of complex organic molecules in cold interstellar clouds
stresses the rich chemical diversity of cold dense cores in stages prior to the
onset of star formation. The detections of ethanol, acetone, and propanal were
made in the framework of QUIJOTE, a deep line survey of TMC-1 in the Q band
that is being carried out with the Yebes 40m telescope. We derive column
densities of (1.1 +/- 0.3)e12 cm-2 for C2H5OH, (1.4 +/- 0.6)e11 cm-2 for
CH3COCH3, and (1.9 +/- 0.7)e11 cm-2 for C2H5CHO. The formation of these three
O-bearing complex organic molecules is investigated with the aid of a detailed
chemical model which includes gas and ice chemistry. The calculated abundances
at a time around 2e5 yr are in reasonable agreement with the values derived
from the observations. The formation mechanisms of these molecules in our
chemical model are as follows. Ethanol is formed on grains by addition of
atomic carbon on methanol followed by hydrogenation and non-thermal desorption.
Acetone and propanal are produced by the gas-phase reaction between atomic
oxygen and two different isomers of the C3H7 radical, where the latter follows
from the hydrogenation of C3 on grains followed by non-thermal desorption. A
gas-phase route involving the formation of (CH3)2COH+ through several
ion-neutral reactions followed by its dissociative recombination with electrons
do also contribute to the formation of acetone.Comment: Accepted for publication in A&
Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN
We report the first laboratory and interstellar detection of the alpha-cyano
vinyl radical (H2CCCN). This species was produced in the laboratory by an
electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne, and its
rotational spectrum was characterized using a Balle-Flygare narrowband-type
Fourier-transform microwave spectrometer operating in the frequency region of
8-40 GHz. The observed spectrum shows a complex structure due to tunneling
splittings between two torsional sublevels of the ground vibronic state, 0+ and
0-, derived from a large-amplitude inversion motion. In addition, the presence
of two equivalent hydrogen nuclei makes necessary to discern between ortho- and
para-H2CCCN. A least squares analysis reproduces the observed transition
frequencies with a standard deviation of ca. 3 kHz. Using the laboratory
predictions, this radical is detected in the cold dark cloud TMC-1 using the
Yebes 40m telescope and the QUIJOTE line survey. The 404-303 and 505-404
rotational transitions, composed of several hyperfine components, were observed
in the 31.0-50.4 GHz range. Adopting a rotational temperature of 6K we derive a
column density of (1.4+/-0.2)e11 cm-2 and (1.1+/-0.2)e11 cm-2 for ortho-H2CCCN
and para-H2CCCN, respectively. The reactions C + CH3CN, and perhaps also N +
CH2CCH, emerge as the most likely routes to H2CCCN in TMC-1.Comment: Accepted for publication in A&A Letters on 18/07/202
Discovery of HCCCH in TMC-1
Based on a novel laboratory method, 14 mm-wave lines of the molecular ion
HCCCH have been measured in high resolution, and the spectroscopic
constants of this asymmetric rotor determined with high accuracy. Using the
Yebes 40 m and IRAM 30 m radio telescopes, we detect four lines of
HCCCH towards the cold dense core TMC-1. With a dipole moment of about
0.55 Debye obtained from high-level ab initio calculations, we derive a column
density of 5.4110 cm and
1.60.510 cm for the ortho and para species,
respectively, and an abundance ratio N(HCCC)/N(HCCCH)= 2.80.7.
The chemistry of HCCCH is modelled using the most recent chemical
network for the reactions involving the formation of HCCCH. We find a
reasonable agreement between model predictions and observations, and new
insights into the chemistry of C bearing species in TMC-1 are obtained
Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN
9 pags., 4 figs., 3 tabs.We report the first laboratory and interstellar detection of the alpha-cyano
vinyl radical (H2CCCN). This species was produced in the laboratory by an
electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne, and its
rotational spectrum was characterized using a Balle-Flygare narrowband-type
Fourier-transform microwave spectrometer operating in the frequency region of
8-40 GHz. The observed spectrum shows a complex structure due to tunneling
splittings between two torsional sublevels of the ground vibronic state, 0+ and
0-, derived from a large-amplitude inversion motion. In addition, the presence
of two equivalent hydrogen nuclei makes necessary to discern between ortho- and
para-H2CCCN. A least squares analysis reproduces the observed transition
frequencies with a standard deviation of ca. 3 kHz. Using the laboratory
predictions, this radical is detected in the cold dark cloud TMC-1 using the
Yebes 40m telescope and the QUIJOTE line survey. The 404-303 and 505-404
rotational transitions, composed of several hyperfine components, were observed
in the 31.0-50.4 GHz range. Adopting a rotational temperature of 6K we derive a
column density of (1.4+/-0.2)e11 cm-2 and (1.1+/-0.2)e11 cm-2 for ortho-H2CCCN
and para-H2CCCN, respectively. The reactions C + CH3CN, and perhaps also N +
CH2CCH, emerge as the most likely routes to H2CCCN in TMC-1.The present study was supported by ERC through the grant ERC-2013-Syg-610256-NANOCOSMOS, Ministry of Science and Technology of Taiwan through project MOST 104-2113-M-009-202, JSPS KAKENHI through Grant 06640644, and Ministerio de Ciencia e Innovación of Spain through projects PID2019-106110GB-I00, PID2019-107115GBC21/AEI/10.13039/501100011033, and PID2019-106235GB-I00. C.C., M.A,
Y.E. and J.C. thank Ministry of Science and Technology of Taiwan and Consejo
Superior de Investigaciones CientÃficas for funding support under the MOSTCSIC Mobility Action 2021 (Grant 11-2927-I-A49-502 and OSTW200006). J.T.
thanks the JSPS Postdoctoral Fellowship for Foreign Researchers and Grant-inAid for JSPS Fellows.Peer reviewe
Planktonic events may cause polymictic-dimictic regime shifts in temperate lakes
Water transparency affects the thermal structure of lakes, and within certain lake depth ranges, it can determine whether a lake mixes regularly (polymictic regime) or stratifies continuously (dimictic regime) from spring through summer. Phytoplankton biomass can influence transparency but the effect of its seasonal pattern on stratification is unknown. Therefore we analysed long term field data from two lakes of similar depth, transparency and climate but one polymictic and one dimictic, and simulated a conceptual lake with a hydrodynamic model. Transparency in the study lakes was typically low during spring and summer blooms and high in between during the clear water phase (CWP), caused when zooplankton graze the spring bloom. The effect of variability of transparency on thermal structure was stronger at intermediate transparency and stronger during a critical window in spring when the rate of lake warming is highest. Whereas the spring bloom strengthened stratification in spring, the CWP weakened it in summer. The presence or absence of the CWP influenced stratification duration and under some conditions determined the mixing regime. Therefore seasonal plankton dynamics, including biotic interactions that suppress the CWP, can influence lake temperatures, stratification duration, and potentially also the mixing regime
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