Abstract
Almost all chemical elements have been made by nucleosynthetic reactions in various kind of stars and have been accumulated along our cosmic history. Among those elements, the origin of ...phosphorus is of extreme interest because it is known to be essential for life such as we know on Earth. However, current models of (Galactic) chemical evolution under-predict the phosphorus we observe in our Solar System. Here we report the discovery of 15 phosphorus-rich stars with unusual overabundances of O, Mg, Si, Al, and Ce. Phosphorus-rich stars likely inherit their peculiar chemistry from another nearby stellar source but their intriguing chemical abundance pattern challenge the present stellar nucleosynthesis theoretical predictions. Specific effects such as rotation or advanced nucleosynthesis in convective-reactive regions in massive stars represent the most promising alternatives to explain the existence of phosphorus-rich stars. The phosphorus-rich stars progenitors may significantly contribute to the phosphorus present on Earth today.
Petroleum, coal and other organics in space Cataldo, Franco; García-Hernández, D. A.; Manchado, Arturo
Astrophysics and space science,
05/2020, Letnik:
365, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The petroleum and coal models of the unidentified infrared emissions (UIE), sometimes referred also as unidentified infrared bands (UIBs) has been reviewed mainly based on the work of the authors ...with the inclusion of unpublished results. It is shown that the petroleum and coal model of the UIE converges and merges quite well with the MAON (Mixed Aromatic Aliphatic Organic Nanoparticles) model of the UIE. It is shown that the thermal treatment of various substrates like PAHs, alkylated PAHs but also mixed aliphatic/olefinic substrates leads invariably to carbonaceous materials matching the infrared spectrum of anthracite coal or certain petroleum fractions. Thus, the experimental thermal processing (which under space conditions could be equivalent to the expected processing by shock waves or high energy radiation) of mixed aromatic/aliphatic organic matter can be used to match also the UIE evolution. Another way to simulate the thermal/radiation processing of organic matter in space, can be achieved through the carbon arc. Simple substrates processed in this way produce carbon soot and a plethora of organic molecules. Fullerenes are found in space both through mid-infrared and optical spectroscopy and it is very likely that other complex related species such as endohedral fullerenes (i.e. fullerenes with a metal, heteroatom or molecules inside the cage) may be formed in space. After all, their formation requires the same conditions as those needed for fullerene formation provided that also a metal vapour (e.g. interstellar/circumstellar gas) is available. The last part of this review is thus dedicated to the recent results on the study and characterization of an endohedral C
60
derivative containing lithium inside the cage.
The radiation-induced polymerization of indene with a γ radiation source was studied at different dose rates (1, 2, 4, 6 kGy/h) and absorbed doses up to 400 kGy. The polymerization rate was ...determined through the thermogravimetric analysis and the spectrophotometric analysis of the irradiated indene solutions. With the two complementary methods the polymerization rates were determined for each dose rate. A mixed polymerization mechanism was ascertained involving either free radicals but also cations. In fact, the mixed mechanism was suggested as well by the n = 0.84 exponent of the dose rate in the polymerization kinetics equation and by the value of the radiation chemical yield G
p
= G(−M) ≈ 10
3
molecules/100 eV. The infrared spectrum of the radiation-polymerized indene is analogous to the spectrum of a reference TiCl
4
-polyindene. However, the FT-IR spectrum of the former shows a couple of better defined and sharper infrared bands with respect to the latter, indicating a better structural regularity for the radio-polyindene. Since indene has been claimed as one of the potential polycyclic aromatic hydrocarbons (PAHs) present in the interstellar medium, our results suggest that it is likely that indene should be accompanied by -polyindene because of the monomer is very sensitive to the high energy radiation-induced polymerization.
The coexistence of a large variety of molecular species (i.e. aromatic, cycloaliphatic and aliphatic) in several astrophysical environments suggests that unidentified infrared emission (UIE) occurs ...from small solid particles containing a mix of aromatic and aliphatic structures (e.g. coal, petroleum, etc.), renewing the astronomical interest on this type of materials. A series of heavy petroleum fractions namely 'distillate aromatic extract', 'Residual Aromatic Extract', heavy aromatic fraction (BQ-1) and asphaltenes derived from BQ-1 were used together with anthracite coal and bitumen as model compounds in matching the band pattern of the emission features of proto-planetary nebulae (PPNe). All the model materials were examined in the mid-infrared (2.5-16.66 μm) and for the first time in the far-infrared (16.66-200 μm), and the infrared bands were compared with the UIE from PPNe. The best match of the PPNe band pattern is offered by the BQ-1 heavy aromatic oil fraction and by its asphaltenes fraction. Particularly interesting is the ability of BQ-1 to match the band pattern of the aromatic-aliphatic C-H stretching bands of certain PPNe, a result which is not achieved neither by the coal model nor by the other petroleum fractions considered here. This study shows that a new interesting molecular model of the emission features of PPNe is asphaltene molecules which are composed by an aromatic core containing three to four condensed aromatic rings surrounded by cycloaliphatic (naphtenic) and aliphatic alkyl chains. Instead, the weakness of the model involving a mixture of polycyclic aromatic hydrocarbons (PAHs) for modelling the aromatic infrared emission bands (AIBs) is shown. The laboratory spectra of these complex organic compounds represent a unique data set of high value for the astronomical community, e.g. they may be compared with the Herschel Space Observatory spectra (∼51-220 μm) of several astrophysical environments such as (proto-) planetary nebulae, H ii regions, reflection nebulae, star-forming galaxies and young stellar objects.
The endohedral fullerene Li@C
60
+
PF
6
−
was characterized by differential scanning calorimetry (DSC), by electronic absorption spectroscopy in the spectral range from 195 to 800 nm and by FT-IR ...and far-infrared spectroscopy. Li@C
60
+
PF
6
−
shows a sharp melting point with the onset at 86 °C and peak at 90 °C and melting enthalpy of 9.5 kJ/mol. The electronic absorption spectrum of Li@C
60
+
PF
6
−
in the UV shows both a hypsochromic shift and a hyperchromic effect with respect to the corresponding electronic transitions of C
60
. In the mid-infrared spectrum Li@C
60
+
cation displays the typical four band pattern of C
60
, with small shifts. The far-infrared spectroscopy appears to be the most effective diagnostic tool to distinguish between C
60
and endohedral fullerenes like Li@C
60
+
. In fact, while C
60
does not show any far-infrared vibration, Li@C
60
+
PF
6
−
shows four far-infrared bands. Also in an astrochemical perspective the search of endohedral fullerenes must rely mainly on the far-infrared spectral region.
The aim of this work is to examine distances to planetary nebulae (PNe) together with other properties that were derived from them, using the astrometry of Gaia Data Release 2 (DR2). We were able to ...identify 1571 objects classified as PNe, for which we assumed distances calculated following a Bayesian statistical approach. From those objects, we selected a sample of PNe with good quality parallax measurements and distance derivations, which we called Golden Astrometry PNe sample (GAPN). In this paper we will review the physical properties of the stars and nebulae in this subsample of PNe.
This paper presents a homogeneous study of abundances in a sample of 79 northern Galactic planetary nebulae (PNe) whose morphological classes have been uniformly determined. Ionic abundances and ...plasma diagnostics were derived from selected optical line strengths in the literature, and elemental abundances were estimated with the ionization correction factor developed by Kingsbourgh & Barlow in 1994. We compare the elemental abundances to the final yields obtained from stellar evolution models of low- and intermediate-mass stars, and we confirm that most bipolar PNe have high nitrogen and helium abundance and are the likely progeny of stars with main-sequence mass greater than 3 M sub( ). We derive (Ne/O) = 0.27 and discuss the implication of such a high ratio in connection with the solar neon abundance. We determine the Galactic gradients of oxygen and neon and found log(O/H)/R = -0.01 dex kpc super(-1) and log(Ne/H)/R = -0.01 dex kpc super(-1). These flat PN gradients are irreconcilable with Galactic metallicity gradients flattening with time.
Oleum (fuming sulphuric acid), a well known superacid, was used as medium for the generation of the radical cation of a series of selected PAHs. The resulting radical cation spectra were studied by ...electronic absorption spectroscopy. Not only common PAHs like naphthalene, anthracene, tetracene, pentacene, perylene, pyrene, benzo
apyrene, phenanthrene and picene were studied but also the less common and very large PAHs relevant also for the astrochemical research, like coronene, hexabenzocoronene, quaterrylene, dicoronylene and a coronene oligomer. A correlation between the first ionization potential (
I
P1) of the PAHs studied and the energy to the so-called A-type band of the radical cations observed in oleum has led to the equation
I
P1
=
1.30
E
A
+
4.39 (in eV) which permits to estimate the energy of the PAHs radical cation transition (
E
A) in the VIS-NIR knowing the relative ionization potential or vice versa.
The thermal behaviour of 21 proteinaceous
l
-amino acids either as pristine samples and also as radiolyzed (3.2 MGy) samples was studied with the differential scanning calorimeter. The onset and peak ...melting point as well as the melting enthalpy of all samples before and after the radiation treatment was measured and reported. The residual amount of each amino acid survived to the radiation dose of 3.2 MGy (
N
γ
) was measured from the melting enthalpies before and after radiolysis and hence the radiation resistance of each amino acid has been determined. The radiolysis causes a systematic reduction of the melting enthalpy and a shift of the onset and peak melting point to lower values. It is shown that
N
γ
does not correlate with the melting points of the amino acids but shows a correlation with the entity of the shift of the melting point peaks occurred after radiolysis. Such correlation instead does not exist between the
N
γ
parameter and the onset melting points of the amino acids. An explanation of such lack of correlation was given. Furthermore, a general relationship has been found between the amino acids melting point peak measured on pristine samples and the melting point peaks after solid state radiolysis. Such relationship can be used to predict roughly the expected melting point after radiolysis at 3.2 MGy of any given amino acid. The last part of the study was dedicated in the attempt to find a correlation between the
N
γ
parameter and the amount of the amino acids survived the radiolysis
R
γ
as measured by spectropolarimetry (ORD spectroscopy). A general trend was found in the connection between the
N
γ
and
R
γ
parameters but not a very strong correlation.
PDF
