scholarly journals First sample of N2H+ nitrogen isotopic ratio measurements in low-mass protostars

2020 ◽  
Vol 644 ◽  
pp. A29
Author(s):  
E. Redaelli ◽  
L. Bizzocchi ◽  
P. Caselli
Keyword(s):  
Gas Phase ◽  
Isotopic Ratio ◽  
Molecular Nitrogen ◽  
Theoretical Models ◽  
Rotational Transition ◽  
Young Stellar Objects ◽  
Isotopic Ratios ◽  
Dust Grains ◽  
Prestellar Cores ◽  
Low Mass

Context. The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and N2H+ is particularly important because it is directly linked to molecular nitrogen N2. However, theoretical models still do not provide an exhaustive explanation for the observed 14N/15N values. Aims. Recent theoretical works suggest that the 14N/15N behaviour is dominated by two competing reactions that destroy N2H+: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if the N2H+ recombination rate is lower with respect to that for N15NH+, the rarer isotopologue is destroyed more quickly. In prestellar cores, due to a combination of low temperatures and high densities, most CO is frozen in ices onto the dust grains, leading to high levels of depletion. On the contrary, in protostellar cores, where temperature are higher, CO ices evaporate back to the gas phase. This implies that the N2H+ isotopic ratio in protostellar cores should be lower than that in prestellar cores, and consistent with the elemental value of ≈440. We aim to test this hypothesis, producing the first sample of N2H+∕N15NH+ measurements in low-mass protostars. Methods. We observe the N2H+ and N15NH+ lowest rotational transition towards six young stellar objects in the Perseus and Taurus molecular clouds. We model the spectra with a custom python code using a constant Tex approach to fit the observations. We discuss in the Appendix the validity of this hypothesis. The derived column densities are used to compute the nitrogen isotopic ratios. Results. Our analysis yields an average of 14N/15N|pro = 420 ± 15 in the protostellar sample. This is consistent with the protosolar value of 440, and significantly lower than the average value previously obtained in a sample of prestellar objects. Conclusions. Our results are in agreement with the hypothesis that, when CO is depleted from the gas-phase, dissociative recombinations with free electrons destroy N15NH+ faster than N2H+, leading to high isotopic ratios in prestellar cores where carbon monoxide is frozen onto dust grains.

scholarly journals A sensitive λ 3 mm line survey of L483

2019 ◽  
Vol 625 ◽  
pp. A147 ◽  
Author(s):  
M. Agúndez ◽  
N. Marcelino ◽  
J. Cernicharo ◽  
E. Roueff ◽  
M. Tafalla
Keyword(s):  
Chemical Composition ◽  
Chemical Characterization ◽  
Isotopic Ratios ◽  
Dark Cloud ◽  
Carbon Chains ◽  
Prestellar Cores ◽  
Low Mass ◽  
Line Survey ◽  
Molecular Abundances

An exhaustive chemical characterization of dense cores is mandatory to our understanding of chemical composition changes from a starless to a protostellar stage. However, only a few sources have had their molecular composition characterized in detail. Here we present a λ 3 mm line survey of L483, a dense core around a Class 0 protostar, which was observed with the IRAM 30 m telescope in the 80–116 GHz frequency range. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud according to their narrow lines (FWHM ~ 0.5 km s−1) and low rotational temperatures (≲10 K). Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH3, CH3OCH3, and C2H5OH, a wide variety of carbon chains, nitrogen oxides like N2O, and saturated molecules like CH3SH, in addition to eight new interstellar molecules (HCCO, HCS, HSC, NCCNH+, CNCN, NCO, H2NCO+, and NS+) whose detection has already been reported. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 and B1-b, and are similar to those in L1527. Apart from the overabundance of carbon chains in TMC-1, we find that L483 does not have a marked chemical differentiation with respect to starless/prestellar cores like TMC-1 and L1544, although it does chemically differentiate from Class 0 hot corino sources like IRAS 16293−2422. This fact suggests that the chemical composition of the ambient cloud of some Class 0 sources could be largely inherited from the dark cloud starless/prestellar phase. We explore the use of potential chemical evolutionary indicators, such as the HNCO/C3S, SO2/C2S, and CH3SH/C2S ratios, to trace the prestellar/protostellar transition. We also derived isotopic ratios for a variety of molecules, many of which show isotopic ratios close to the values for the local interstellar medium (remarkably all those involving 34S and 33S), while there are also several isotopic anomalies like an extreme depletion in 13C for one of the two isotopologs of c-C3H2, a drastic enrichment in 18O for SO and HNCO (SO being also largely enriched in 17O), and different abundances for the two 13C substituted species of C2H and the two 15N substituted species of N2H+. We report the first detection in space of some minor isotopologs like c-C3D. The exhaustive chemical characterization of L483 presented here, together with similar studies of other prestellar and protostellar sources, should allow us to identify the main factors that regulate the chemical composition of cores along the process of formation of low-mass protostars.

scholarly journals Infalling Streamer-Disk-Outflow System in a Nearby High-mass Star Formation Region

2021 ◽  
Author(s):  
Xi Chen ◽  
Zhiyuan Ren ◽  
Da-Lei Li ◽  
Tie Liu ◽  
Ke Wang ◽  
...  
Keyword(s):  
Direct Detection ◽  
Theoretical Models ◽  
Young Stellar Objects ◽  
High Mass ◽  
Similar Process ◽  
Mass Star ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Stellar Objects ◽  
Low Mass

Abstract Theoretical models and numerical simulations suggest that high mass star (with mass > 8 solar mass) can be formed either via monolithic collapse of a massive core or competitive accretion, but the dominant mechanism is currently unclear. Although recent high resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have detected physical and kinematic features, such as disks, outflows and filamentary structures surrounding the high mass young stellar objects (HMYSO), direct detection of the infalling gas towards the HMYSO is still the key to distinguish the different scenarios. Chemically fresh gas inflows have been detected towards low-mass stars being formed, which are consistent with the accretion-disk-outflow process. In this work we report the detection of a chemically fresh inflow which is feeding HMYSO growth in the nearby high mass star-forming region G352.63-1.07. High quality images of the dust and molecular lines from both ALMA and the Submillimeter Array (SMA) have consistently revealed a gravitationally-controlled gas inflow towards a rotating structure (disk or torus) around the HMYSO. The HMYSO is also observed to have an outflow, but it can be clearly separated from the inflow. These kinematic features provide observational evidence to support the conjecture that high-mass stars can be formed in a similar process to that observed in the low-mass counterparts. The chemically fresh infalling streamers could also be related with the disk configuration, fragmentation and accretion bursts that occur in both simulations and observations.

scholarly journals Low-mass star formation and subclustering in the H II regions RCW 32, 33, and 27 of the Vela Molecular Ridge

2018 ◽  
Vol 617 ◽  
pp. A63 ◽  
Author(s):  
L. Prisinzano ◽  
F. Damiani ◽  
M. G. Guarcello ◽  
G. Micela ◽  
S. Sciortino ◽  
...  
Keyword(s):  
Star Formation ◽  
Cluster Formation ◽  
Large Population ◽  
Circumstellar Disks ◽  
Theoretical Models ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Northwestern Region ◽  
Low Mass ◽  
Young Clusters

Context. Most stars are born in clusters, and recent results suggest that star formation (SF) preferentially occurs in subclusters. Studying the morphology and SF history of young clusters is crucial for understanding early cluster formation processes. Aims. We aim to identify the embedded population of young stellar objects (YSOs) down to the low-mass stars in the M-type regime in the three H II regions RCW 33, RCW 32, and RCW 27, which are located in the northwestern region of the Vela Molecular Ridge. Our aim is to characterize their properties, such as morphology and extent of the clusters in the three H II regions, derive stellar ages, and determine the connection of the SF history with the environment. Methods. Through public photometric surveys such as Gaia, VPHAS+, 2MASS, and Spitzer/GLIMPSE, we identify YSOs with classical techniques aimed at detecting IR, Hα, and UV excesses as signatures of circumstellar disks and accretion. In addition, we implement a method for distinguishing main-sequence (MS) stars and giants in the M-type regime by comparing the reddening derived in several optical/IR color-color diagrams, assuming suitable theoretical models. Since this diagnostic is sensitive to stellar gravity, the procedure allows us to also identify pre-MS (PMS) stars. Results. Using the classical membership criteria, we find that a large population of YSOs shows signatures of circumstellar disks with or without accretion. In addition, with the new technique of M-type star selection, we find a rich population of young M-type stars whose spatial distribution strongly correlates with the more massive population. We find evidence of three young clusters, with different morphology, for which we estimate the individual distances using TGAS Gaia data of the brighter subsample. In addition, we identify field stars falling in the same region by securely classifying them as giants and foreground MS stars. Conclusions. We identify the embedded population of YSOs down to about 0.1 M⊙ that is associated with the three H II regions RCW 33, RCW 32, and RCW 27 and the three clusters Vela T2, Cr 197, and Vela T1, respectively. All the three clusters are located at a similar distance, but they have very different morphologies. Our results suggest a decreasing SF rate in Vela T2 and triggered SF in Cr 197 and Vela T1.

scholarly journals Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

2019 ◽  
Vol 632 ◽  
pp. L12 ◽  
Author(s):  
P. Hily-Blant ◽  
V. Magalhaes de Souza ◽  
J. Kastner ◽  
T. Forveille
Keyword(s):  
Solar System ◽  
Isotopic Ratio ◽  
Giant Planet ◽  
Rotational Transition ◽  
Kinetic Temperature ◽  
Isotopic Ratios ◽  
Fractionation Process ◽  
Spatially Resolved ◽  
T Tauri ◽  
Solar System Bodies

The isotopic ratio of nitrogen measured in primitive Solar System bodies shows a broad range of values, the origin of which remains unknown. One key question is whether these isotopic reservoirs of nitrogen predate the comet formation stage or are posterior to it. Another central question is elucidating the processes that can produce the observed variations in the 14N/15N isotopic ratio. Disks that orbit pre-main-sequence (T Tauri) stars provide unique opportunities for observing the chemical content of analogs of the protosolar nebula and therefore for building a comprehensive scenario that can explain the origin of nitrogen in the Solar System and in planet-forming disks. With ALMA, it has become possible to measure isotopic ratios of nitrogen-bearing species in such environments. We present spectrally and spatially resolved observations of the hyperfine structure of the 4−3 rotational transition of HCN and its main isotopologs H13CN and HC15N in the disk orbiting the 8 Myr old T Tauri star TW Hya. The sensitivity allows directly measuring the HCN/H13CN and HCN/HC15N abundance ratios with minimal assumptions. Averaged spatially over the disks, the ratios are 86 ± 4 and 223 ± 21, respectively. The latter value is significantly lower than the CN/C15N ratio of 323 ± 30 in this disk and thus provides the first evidence that two isotopic reservoirs of nitrogen are present in a disk at the stage of giant planet and comet formation. Furthermore, we find clear evidence for an increase in the ratio of HCN to HC15N with radius. The ratio in the outer disk, at 45 au, is 339 ± 28, in excellent agreement with direct measurements in the local interstellar medium, and with the bulk nitrogen isotopic ratio predicted from galactic evolution calculations. In the comet formation region at r = 20 au, the ratio is a factor ≈3 lower, 121 ± 11. This radial increase qualitatively agrees with the scenario in which selective photodissociation of N2 is the dominant fractionation process. However, our isotopic ratios and kinetic temperature of the HCN-emitting layers quantitatively disagree with models of nitrogen chemistry in disks.

Volatile depletion and evolution of Vesta from coupled Cu-Zn isotope systematics

2021 ◽  
Author(s):  
Jasmeet K. Dhaliwal ◽  
James M.D. Day ◽  
John B. Creech ◽  
Frederic Moynier
Keyword(s):  
Isotopic Ratio ◽  
Parent Body ◽  
Isotopic Ratios ◽  
The Moon ◽  
Magmatic Differentiation ◽  
Isotopic Compositions ◽  
Zinc Isotope ◽  
Zn Concentration ◽  
Low Mass ◽  
Cu And Zn

<p>The moderately volatile elements, Cu and Zn, are not strongly affected by magmatic differentiation [1, 2] and are important tracers of volatile depletion in planetary bodies, particularly low-mass, airless bodies [3]. New isotopic ratio and abundance measurements for both Cu and Zn are presented for eucrites to more fully understand volatile depletion processes that affected the parent-body of the howardite-eucrite-diogenite (HED) meteorites, the asteroid 4-Vesta. Zinc isotope ratios are reported for twenty-eight eucrite samples, which along with prior data [4] yield a range of δ<sup>66</sup>Zn from -1.8 to +6.3 ‰, excluding one outlier, PCA 82502 (δ<sup>66</sup>Zn = -7.8 ‰) and a Zn concentration range from 0.3 to 3.8 p.p.m. Heavy Zn isotopic ratios (positive δ<sup>66</sup>Zn compositions) in eucrites form a negative trend with Zn concentration, reflecting volatile depletion processes on Vesta that are similar to the Moon [5, 6]. Within the combined sample set, eleven eucrites have light Zn isotopic compositions from δ<sup>66</sup>Zn of -0.02 to -7.8 ‰, with the majority having more negative compositions than likely chondritic precursors (maximum δ<sup>66</sup>Zn of ~ -0.2 ‰ [7]). These samples are interpreted to reflect condensates formed subsequent to surface volatilization and outgassing, such as during impact bombardment. Measurements of Cu compositions are also reported for nineteen of the samples, yielding a range of δ<sup>65</sup>Cu from -1.6 to +0.9 ‰, and range of Cu concentrations from 0.2 to 2.8 p.p.m., with the exception of Stannern (Cu > 10 ppm). As with Zn, negative Cu isotopic ratios that are lighter than chondritic compositions (δ<sup>65</sup>Cu ~ -0.5 ‰ [8]) are attributed to recondensation that occurred following impact-induced vaporization (cf. [9]). Within the wide ranges of Zn and Cu isotopic compositions measured in eucrites, most samples cluster within ~ 0 ‰ < δ<sup>66</sup>Zn < +3 ‰ and ~ 0.2 ‰ < δ<sup>65</sup>Cu < +0.9 ‰. This range is interpreted to reflect volatile depletion processes similar to those that affected the Moon (BSM: δ<sup>66</sup>Zn +1.4 ± 0.5‰ [5, 6, 10, 11] and δ<sup>65</sup>Cu = +0.92 ± 0.16‰ [9-11]). The greater heterogeneity in eucrite Zn and Cu isotopic compositions compared to lunar samples can be attributed to the smaller size of the HED parent asteroid, which may have experienced more limited homogenization of these signatures following volatile depletion and for eucrites which have experienced complex impact addition and metamorphic processes.  </p><p>[1] Chen et al. (2013) EPSL, 369, 34-42. [2] Savage et al. (2015) Geochemical Perspective Letters, 1, 53-64. [3] Day and Moynier (2014) Philisophical Transactions of the Royal Society A, 372, p.20130259. [4] Paniello et al. (2012) GCA, 86, 76-87. [5] Paniello et al. (2012) Nature, 490, 376-379. [6] Kato et al. 2015 Nature Communications, 6, 1-4. [7] Luck et al. (2005) GCA 69, 5351-5363. [8] Luck et al. (2003) GCA, 67¸143-151. [9] Day et al. (2019) GCA, 266, 131-143. [10] Moynier et al. (2006) GCA, 70, 6103-6117. [11] Herzog et al. (2009) GCA, 73, 5884-5904.</p>

scholarly journals ALMA view of the 12C/13C isotopic ratio in starburst galaxies

2019 ◽  
Vol 629 ◽  
pp. A6 ◽  
Author(s):  
X. D. Tang ◽  
C. Henkel ◽  
K. M. Menten ◽  
Y. Gong ◽  
S. Martín ◽  
...  
Keyword(s):  
Gas Phase ◽  
Isotopic Ratio ◽  
Outer Part ◽  
Starburst Galaxies ◽  
Molecular Gas ◽  
Isotopic Ratios ◽  
Processed Material ◽  
Central Regions ◽  
Ngc 1068 ◽  
Nuclear Regions

We derive molecular-gas-phase 12C/13C isotope ratios for the central few hundred parsecs of the three nearby starburst galaxies NGC 253, NGC 1068, and NGC 4945 making use of the λ ∼ 3 mm 12CN and 13CN N = 1–0 lines in the ALMA Band 3. The 12C/13C isotopic ratios derived from the ratios of these lines range from 30 to 67 with an average of 41.6 ± 0.2 in NGC 253, from 24 to 62 with an average of 38.3 ± 0.4 in NGC 1068, and from 6 to 44 with an average of 16.9 ± 0.3 in NGC 4945. The highest 12C/13C isotopic ratios are determined in some of the outskirts of the nuclear regions of the three starburst galaxies. The lowest ratios are associated with the northeastern and southwestern molecular peaks of NGC 253, the northeastern and southwestern edge of the mapped region in NGC 1068, and the very center of NGC 4945. In the case of NGC 1068, the measured ratios suggest inflow from the outer part of NGC 1068 into the circum-nuclear disk through both the halo and the bar. Low 12C/13C isotopic ratios in the central regions of these starburst galaxies indicate the presence of highly processed material.

scholarly journals Chemical Characteristics of Embedded Young Stellar Objects

2000 ◽  
Vol 197 ◽  
pp. 71-80
Author(s):  
Michiel R. Hogerheijde
Keyword(s):  
Gas Phase ◽  
Surface Reactions ◽  
Young Stellar Objects ◽  
Chemical Characteristics ◽  
Dust Grains ◽  
Gas Phase Reactions ◽  
Stellar Objects ◽  
Grain Surface ◽  
Theoretical Considerations

Based on theoretical considerations, the chemistry around embedded young stellar objects is expected to be governed by the interplay between gas-phase reactions, condensation of molecules onto dust grains, grain surface reactions, and evaporation of altered ice mantles near the star and in the outflow. I discuss the chemical characteristics of embedded young stellar objects, with special emphasis on these processes.

scholarly journals Precursors of complex organic molecules: NH3 and CH3OH in the ices surrounding low-mass protostars

2008 ◽  
Vol 4 (S251) ◽  
pp. 105-110 ◽  
Author(s):  
Sandrine Bottinelli ◽  
Adwin C. A. Boogert ◽  
Ewine F. van Dishoeck ◽  
Martha Beckwith ◽  
Jordy Bouwman ◽  
...  
Keyword(s):  
Solid State ◽  
Gas Phase ◽  
Organic Molecules ◽  
High Sensitivity ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Space Telescope ◽  
Low Mass ◽  
Complex Organic

AbstractNH3 and CH3OH are key molecules in the chemical networks leading to the formation of complex N- and O-bearing organic molecules. However, despite a number of recent studies, there is still a lot to learn about their abundances in the solid state and how they relate to those of other N/O-bearing organic molecules or to NH3 and CH3OH abundances in the gas phase. This is particularly true in the case of low-mass young stellar objects (YSOs), for which only the recent advent of the Spitzer Space Telescope has allowed high sensitivity observations of the ices in their enveloppes. We present a combined study of Spitzer data (obtained within the Legacy program “From Molecular Cores to Planet-Forming Disks”, c2d) and laboratory spectra, leading to the detections of NH3 and CH3OH in the ices of low-mass protostars. We investigate correlations with other ice features and conclude with prospects on further studies linking these two precursors of complex organic molecules with their gas-phase products.

scholarly journals The Observational Evidence for Accretion

1997 ◽  
Vol 182 ◽  
pp. 391-405 ◽  
Author(s):  
Lee Hartmann
Keyword(s):  
Large Range ◽  
Observational Evidence ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
T Tauri ◽  
Accretion Rates ◽  
Low Mass ◽  
Stellar Magnetospheres ◽  
Mass Ejection

Outflows from low-mass young stellar objects are thought to draw upon the energy released by accretion onto T Tauri stars. I briefly summarize the evidence for this accretion and outline present estimates of mass accretion rates. Young stars show a very large range of accretion rates, and this has important implications for both mass ejection and for the structure of stellar magnetospheres which may truncate T Tauri disks.

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