Radiolysis of ammonia-containing ices by energetic, heavy and highly charged ions inside dense astrophysical environments

Deeply inside dense molecular clouds and protostellar disks, the interstellar ices are protected from stellar energetic UV photons. However, X-rays and energetic cosmic rays can penetrate inside these regions triggering chemical reactions, molecular dissociation and evaporation processes. We present experimental studies on the interaction of heavy, highly charged and energetic ions (46 MeV Ni^13+) with ammonia-containing ices in an attempt to simulate the physical chemistry induced by heavy ion cosmic rays inside dense astrophysical environments. The measurements were performed inside a high vacuum chamber coupled to the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France.\textit{In-situ} analysis is performed by a Fourier transform infrared spectrometer (FTIR) at different fluences. The averaged values for the dissociation cross section of water, ammonia and carbon monoxide due to heavy cosmic ray ion analogs are ~2x10^{-13}, 1.4x10^{-13} and 1.9x10^{-13} cm$^2$, respectively. In the presence of a typical heavy cosmic ray field, the estimated half life for the studied species is 2-3x10^6 years. The ice compaction (micropore collapse) due to heavy cosmic rays seems to be at least 3 orders of magnitude higher than the one promoted by (0.8 MeV) protons . In the case of the irradiated H2O:NH3:CO ice, the infrared spectrum at room temperature reveals five bands that were tentatively assigned to vibration modes of the zwitterionic glycine (+NH3CH2COO-).Comment: Accepted to be published in Astronomy and Astrophysics; Number of pages: 12; Number of Figures: 7; Number of Tables:

The Occurrence of Rocky Habitable-zone Planets around Solar-like Stars from Kepler Data

We present the occurrence rates for rocky planets in the habitable zones (HZs) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define η⊕ as the HZ occurrence of planets with radii between 0.5 and 1.5 R⊕ orbiting stars with effective temperatures between 4800 and 6300 K. We find that η⊕ for the conservative HZ is between 0.37^(+0.48)_(−0.21) (errors reflect 68% credible intervals) and 0.60^(+0.90)_(−0.36) planets per star, while the optimistic HZ occurrence is between 0.58^(+0.73)_(−0.33) and 0.88^(+1.28)_(−0.51) planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates between using Poisson likelihood Bayesian analysis and using Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with 95% confidence that, on average, the nearest HZ planet around G and K dwarfs is ~6 pc away and there are ~4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun

The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data

We present occurrence rates for rocky planets in the habitable zones (HZ) of main-sequence dwarf stars based on the Kepler DR25 planet candidate catalog and Gaia-based stellar properties. We provide the first analysis in terms of star-dependent instellation flux, which allows us to track HZ planets. We define $\eta_\oplus$ as the HZ occurrence of planets with radius between 0.5 and 1.5 $R_\oplus$ orbiting stars with effective temperatures between 4800 K and 6300 K. We find that $\eta_\oplus$ for the conservative HZ is between $0.37^{+0.48}_{-0.21}$ (errors reflect 68\% credible intervals) and $0.60^{+0.90}_{-0.36}$ planets per star, while the optimistic HZ occurrence is between $0.58^{+0.73}_{-0.33}$ and $0.88^{+1.28}_{-0.51}$ planets per star. These bounds reflect two extreme assumptions about the extrapolation of completeness beyond orbital periods where DR25 completeness data are available. The large uncertainties are due to the small number of detected small HZ planets. We find similar occurrence rates using both a Poisson likelihood Bayesian analysis and Approximate Bayesian Computation. Our results are corrected for catalog completeness and reliability. Both completeness and the planet occurrence rate are dependent on stellar effective temperature. We also present occurrence rates for various stellar populations and planet size ranges. We estimate with $95\%$ confidence that, on average, the nearest HZ planet around G and K dwarfs is about 6 pc away, and there are about 4 HZ rocky planets around G and K dwarfs within 10 pc of the Sun.Comment: To appear in The Astronomical Journa

Spectrophotometric analysis of the T Tauri star GQ Lupi A

Context. GQ Lup A is a classical T Tauri star that shows clear signs of accretion through the presence of inverse P Cygni profiles in its main emission lines. Recently, Neuhäuser et al. (2005, A&A, 435, L13) found a co-moving sub-stellar companion of GQ Lup A, raising the importance of determining precise stellar parameters, system age, and distance to GQ Lup. Aims. Our main objective is to use spectrophotometric time series to determine GQ Lup A stellar parameters and predict its photospheric spectral distribution. The excess spectral luminosity can then be measured and employed to test predictions of magnetospheric accretion models of classical T Tauri stars. Methods. We present the analysis of 18 spectrophotometric observations of the T Tauri star GQ Lup A (K7) obtained with the Boller & Chivens spectrograph at the 1.52 m ESO telescope in La Silla. We also revisited archival photometric data of this star, comparing previous light curve variability with our more recent data. Results. We determined the photospheric flux of GQ Lup A on each observing night and obtained the stellar radius ($R_{\star}$ = 1.8  ±  0.3 $R_{\odot}$), adopting a mean distance of 150 ± 20 pc to the Lupus 1 cloud. Assuming a K7 V temperature of 4060 K, the luminosity of GQ Lup A is $L_{\star}$ = 0.8 ± 0.3 $L_{\odot}$. Standard evolutionary models indicate a stellar mass of $M_{\star}$ = 0.8 ± 0.2 $M_{\odot}$ and an age of 3 ± 2 Myr. GQ Lup A spectral lines are consistent with a projected rotational velocity of $v\sin i$    =  6.5 ± 2.0  km s-1. We measured the excess emission – veiling – and used the resulting photospheric spectral distribution to calculate a stellar extinction (AV) of 0.5 ± 0.1. The veiling was found to be variable and periodic at 10.7 ± 1.6 days, which is consistent with the period of GQ Lup A obtained from archival B band photometric data (10.43 ± 0.12 days). The star exhibits strong emission lines with substantial variability in flux. The emission line fluxes are strongly correlated with one another but not with veiling

Decomposition of the CO stretching vibration band of laboratory H2O-CO ices irradiated by heavy ions

International audienceAbstract H2O and CO molecules are the main constituents of the interstellar dust grain ice mantles. Infrared spectra of the ices in line of sights of young stellar objects and background stars have shown that the CO stretching vibration band can be decomposed into three main components: 2143, 2139 and 2136 cm−1, assigned to CO in different environment sites. The relative strengths between the components have been associated to an evolutionary track of the interstellar molecular clouds. H2O:CO (3:2) and (10:1) ices samples were irradiated by 0.79 MeV/u 58Ni13 + ions to simulate the effects produced by heavy ion cosmic rays in typical interstellar ices mixtures. The CO stretching vibration band is decomposed into six Gaussians functions (2150, 2144, 2141, 2138, 2136 and 2133 cm−1) and their integrated absorbances were measured as a function of fluence. The results have shown that, at the final fluence, the component 2138 cm−1 is the main component of the CO stretching vibration band. The component 2150 cm−1 disappears at the beginning of irradiation. Based on the present and previous results, a time scale for the components in the interstellar ices is proposed. For H2O:CO ice in the ISM it is predicted that, after 1 Myrs, the main components of the CO stretching vibration band are the 2138 cm−1 and 2141 cm−1, due to the CO monomers and dimers, respectively

Laboratory simulation of heavy-ion cosmic-ray interaction with condensed CO

International audienceContext. Within dense interstellar clouds, from their periphery to regions deep inside, ice mantles on dust grains are exposed to cosmic-ray irradiation. Various swift ions contribute from protons to iron in the keV to TeV energy range. Observations show that in some lines of sight condensed CO molecules are an important component of the ice. Aims. We irradiate CO ices with Ni ions of relatively high energy (50 and 537 MeV) to simulate the effects produced by fast heavy cosmic-ray ions in interstellar grain mantles. Methods. CO gas is condensed on a CsI substrate at 13 K and irradiated by 50 MeV 58Ni13+ and 537 MeV 64Ni24+ ions up to a final fluence of ≈1 × 1013 cm−2, at a flux of 1 × 109 cm−2 s−1. The sputtering yields, the destruction rate of CO, and the rate of formation of new molecular species are measured in situ by Fourier transform infrared spectroscopy (FTIR). Results. The measured CO destruction cross-sections and sputtering yields induced by Ni ions are, respectively, (i) for 50 MeV, σd = 1.0×10−13 cm2 and Y = 7×104 molecules/impact; (ii) for 537 MeV, σd = 3.0×10−14 cm2 and Y = 5.85×104 molecules/impact. Based on the present and previous results, the desorption rates induced by H, Ni, and Fe ions are estimated for a wide range of energies. The contribution of the heavy ions is found to dominate over that of protons in the interstellar medium

Chemical reactions in H2O:CO interstellar ice analogs promoted by energetic heavy ion irradiation

International audienceH 2 O:CO, at concentrations of (3:2) and (10:1), was condensed on CsI substrate at 15 K and irradiated with 46 MeV 58 Ni 11+ ion beam. Radiolysis induced by fast heavy ions was analyzed by infrared spectroscopy (FTIR). The formation of nine molecular species, CO 2 , H 2 O 2 , HCOOH, HCO, H 2 CO, 13 CO 2 , CH 3 OH, O 3 and C 3 O 2 was observed. For both concentrations, carbon dioxide (CO 2), formaldehyde (H 2 CO), formic acid (HCOOH), and hydrogen peroxide (H 2 O 2) are the most abundant products species, and tricarbon dioxide (C 3 O 2) is much less abundant. Precursor destruction cross sections and formation cross sections of products are determined. The CO destruction cross section for the (3:2) concentration is almost five times higher than that of water, while those for the (10:1) concentration are practically the same. Atomic sputtering yields are estimated for the two ice films, the total mass sputtered is approximately 2.5 × 10 6 u per impact. These results contribute to figure out the chemical pathways of compounds synthesized from the two most abundant organic species (H 2 O and CO) observed in the ices of grain mantles of the circumstellar envelopes and interstellar medium. In additional, the finding results reveal that molecular astronomical percentages are comparable to those obtained after 15 eV molec −1 of deposited dose in current experiments compared with the relative concentration of molecules in solid phase observed in MYSO, LYSO, BG Stars, and Comets

CHEMICAL PROCESSING OF PURE AMMONIA AND AMMONIA-WATER ICES INDUCED BY HEAVY IONS

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