14 research outputs found
A 10- YSO with a Keplerian disk and a nonthermal radio jet
We previously observed the star-forming region G16.590.05 through
interferometric observations of both thermal and maser lines, and identified a
high-mass young stellar object (YSO) which is surrounded by an accretion disk
and drives a nonthermal radio jet. We performed high-angular-resolution (beam
FWHM ~0.15") 1.2-mm continuum and line observations towards G16.590.05 with
the Atacama Large Millimeter Array (ALMA). The main dust clump, with size
~10 au, is resolved into four relatively compact (diameter ~2000 au)
millimeter (mm) sources. The source harboring the high-mass YSO is the most
prominent in molecular emission. By fitting the emission profiles of several
unblended and optically thin transitions of CHOCH and CHOH, we
derived gas temperatures inside the mm-sources in the range 42--131 K, and
calculated masses of 1--5 . A well-defined Local Standard of Rest
velocity (Vlsr) gradient is detected in most of the high-density molecular
tracers at the position of the high-mass YSO, pinpointed by compact 22-GHz
free-free emission. This gradient is oriented along a direction forming a large
(~70 degree) angle with the radio jet, traced by elongated 13-GHz continuum
emission. The butterfly-like shapes of the P-V plots and the linear pattern of
the emission peaks of the molecular lines at high velocity confirm that this
Vlsr gradient is due to rotation of the gas in the disk surrounding the
high-mass YSO. The disk radius is ~500 au, and the Vlsr distribution along the
major axis of the disk is well reproduced by a Keplerian profile around a
central mass of 102 . The position of the YSO is offset by >~
0.1" from the axis of the radio jet and the dust emission peak. To explain this
displacement we argue that the high-mass YSO could have moved from the center
of the parental mm source owing to dynamical interaction with one or more
companions.Comment: 16 pages, 12 figures, accepted by Astronomy & Astrophysics, Main
Journa
La caccia al fosforo interstellare, lâelemento pre-biotico dimenticato
Il fosforo Ăš un elemento cruciale per lo sviluppo della vita come la conosciamo, ma a causa della sua bassa abbondanza cosmica, fino a pochi anni fa la sua chimica interstellare era quasi del tutto sconosciuta. Dal 2016, il gruppo di Formazione Stellare di Arcetri ha contribuito in modo fondamentale alla comprensione di alcuni processi astrochimici che coinvolgono questo elemento in regioni della Galassia in cui si formano nuove stelle, aprendo la strada a un numero crescente di studi su questo elemento pre-biotico finora âdimenticatoâ.Phosphorus is a crucial element for the development of life as we know it, but because of its low cosmic abundance, until recently its interstellar chemistry was almost totally unknown. Since 2016, the star formation group at Arcetri has made a fundamental contribution to our understanding of the astrochemical processes that involve this element in the star-forming regions of the Galaxy, paving the way for a growing number of studies on this pre-biotic element that had been âforgottenâ up to now
A sequential acid-base (SAB) mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds
The abundance ratios between isomers of a COM observed in the ISM provides
valuable information about the chemistry and physics of the gas and eventually,
the history of molecular clouds. In this context, the origin of an abundance of
c-HCOOH acid of only 6% the isomer c-HCOOH abundance in cold cores, remains
unknown. Herein, we explain the presence of c-HCOOH in dark molecular clouds
through the destruction and back formation of c-HCOOH and t-HCOOH in a cyclic
process that involves HCOOH and highly abundant molecules such as HCO+ and NH3.
We use high-level ab initio methods to compute the potential energy profiles
for the cyclic destruction/formation routes of c-HCOOH and t-HCOOH. Global rate
constants and branching ratios were calculated based on the transition state
theory and the master equation formalism under the typical conditions of the
ISM. The destruction of HCOOH by reaction with HCO+ in the gas phase leads to
three isomers of the cation HC(OH)2+. The most abundant cation can react in a
second step with other abundant molecules of the ISM like NH3 to form back
c-HCOOH and t-HCOOH. This mechanism explains the formation of c-HCOOH in dark
molecular clouds. Considering this mechanism, the fraction of c-HCOOH with
respect t-HCOOH is 25.7%. To explain the 6% reported by the observations we
propose that further destruction mechanisms of the cations of HCOOH should be
taken into account. The sequential acid-base (SAB) mechanism proposed in this
work involves fast processes with very abundant molecules in the ISM. Thus,
HCOOH very likely suffers our proposed transformations in the conditions of
dark molecular clouds. This is a new approach in the framework of the isomerism
of organic molecules in the ISM which has the potential to try to explain the
ratio between isomers of organic molecules detected in the ISM
Precursors of fatty alcohols in the ISM: Discovery of n-propanol
Theories on the origins of life propose that early cell membranes were
synthesized from amphiphilic molecules simpler than phospholipids such as fatty
alcohols. The discovery in the interstellar medium (ISM) of ethanolamine, the
simplest phospholipid head group, raises the question whether simple
amphiphilic molecules are also synthesized in space. We investigate whether
precursors of fatty alcohols are present in the ISM. For this, we have carried
out a spectral survey at 7, 3, 2 and 1 mm toward the Giant Molecular Cloud
G+0.693-0.027 located in the Galactic Center using the IRAM 30m and Yebes 40m
telescopes. Here, we report the detection in the ISM of the primary alcohol
n-propanol (in both conformers Ga-n-C3H7OH and Aa-n-C3H7OH), a precursor of
fatty alcohols. The derived column densities of n-propanol are (5.5+-0.4)x10^13
cm^-2 for the Ga conformer and (3.4+-0.3)x10^13 cm^-2 for the Aa conformer,
which imply molecular abundances of (4.1+-0.3)x10^-10 for Ga-n-C3H7OH and of
(2.5+-0.2)x10^-10 for Aa-n-C3H7OH. We also searched for the AGa conformer of
n-butanol (AGa-n-C4H9OH) without success yielding an upper limit to its
abundance of <4.1x10^-11. The inferred CH3OH:C2H5OH:C3H7OH:C4H9OH abundance
ratios go as 1:0.04:0.006:<0.0004 toward G+0.693-0.027, i.e. they decrease
roughly by one order of magnitude for increasing complexity. We also report the
detection of both syn and anti conformers of vinyl alcohol, with column
densities of (1.11+-0.08)x10^14 cm^-2 and (1.3+-0.4)x10^13 cm^-2, and
abundances of (8.2+-0.6)x10^-10 and (9.6+-3.0)x10^-11, respectively. The
detection of n-propanol, together with the recent discovery of ethanolamine in
the ISM, opens the possibility that precursors of lipids according to theories
of the origin of life, could have been brought to Earth from outer space.Comment: 15 pages, 10 figures, accepted for A&
Extreme radio flares and associated X-ray variability from young stellar objects in the Orion Nebula Cluster
Jan Forbrich, et al, âExtreme Radio Flares and Associated XRay Variability from Young Stellar Objects in the Orion Nebula Clusterâ, The Astrophysical Journal, Vol. 844 (2), July 2017. DOI: https://doi.org/10.3847/1538-4357/aa7aa4. © 2017 The American Astronomical Society. All Rights Reserved.Young stellar objects are known to exhibit strong radio variability on timescales of weeks to months, and a few reports have documented extreme radio flares with at least an order of magnitude change in flux density on timescales of hours to days. However, there have been few constraints on the occurrence rate of such radio flares or on the correlation with pre-main sequence X-ray flares, although such correlations are known for the Sun and nearby active stars. Here we report simultaneous deep VLA radio and Chandra X-ray observations of the Orion Nebula Cluster, targeting hundreds of sources to look for the occurrence rate of extreme radio variability and potential correlation with the most extreme X-ray variability. We identify 13 radio sources with extreme radio variability, with some showing an order of magnitude change in flux density in less than 30 minutes. All of these sources show X-ray emission and variability, but we find clear correlations with extreme radio flaring only on timescales <1 hr. Strong X-ray variability does not predict the extreme radio sources and vice versa. Radio flares thus provide us with a new perspective on high-energy processes in YSOs and the irradiation of their protoplanetary disks. Finally, our results highlight implications for interferometric imaging of sources violating the constant-sky assumption.Peer reviewedFinal Published versio
Proceedings of Abstracts, School of Physics, Engineering and Computer Science Research Conference 2022
© 2022 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Plenary by Prof. Timothy Foat, âIndoor dispersion at Dstl and its recent application to COVID-19 transmissionâ is © Crown copyright (2022), Dstl. This material is licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] present proceedings record the abstracts submitted and accepted for presentation at SPECS 2022, the second edition of the School of Physics, Engineering and Computer Science Research Conference that took place online, the 12th April 2022
Phosphorus in the interstellar medium: the missing prebiotic element
<p>Phosphorus (P) is a crucial element for prebiotic chemistry and for the<br>
development of life in the Universe. It is one of the key components of deoxyri-<br>
bonucleic acid (DNA), phospholipids (the structural components of all cellular<br>
membranes) and the adenosine triphosphate (ATP) molecule, from which all<br>
forms of life assume energy. The Chemistry Nobel Prize Sir Alexander Todd remarked the astrobiological importance of P when he said: âWhere thereâs life,<br>
thereâs phosphorusâ. For these reasons, the study of interstellar phosphorus is<br>
generating increasing interest in the last years. It is mandatory its study in<br>
star-forming regions, where stars, planets (and eventually life) are expected to<br>
arise. However, our knowledge about P in the interstellar medium is still very<br>
poor. For this, our group started several observational and theoretical projects<br>
to study P-bearing species in star-forming regions. In my talk I will present the<br>
the first detections of P-O - key chemical bond to build-up the DNA double<br>
helix - towards two star-forming regions, and multiple detections of PN towards<br>
a large sample of massive dense cores. The observed molecular abundances<br>
indicates that P is significantly more abundant in star-forming regions than<br>
previously thought. I will also show the results of recent ALMA and IRAM 30m<br>
telescope observations of selected massive cores in the Galactic Disk and several<br>
clouds in the Galactic Center, which suggest that shocks may have a key role<br>
to sputtering P from grain mantles and to explain the observed abundances of<br>
P-bearing molecules in the gas-phase. All these findings are helping us to attain<br>
a much better understanding about the unknown chemistry of P in space.</p