Deuterium fractionation and CO depletion in Barnard 5

Abstract

Deuterium fractionation provides a key diagnostic of the physical and chemical evolution of prestellar and protostellar cores, where it is strongly linked to CO depletion in cold, dense gas. We present the first spatially resolved maps of deuterium fraction and CO depletion in the Barnard 5 (B5) region of the Perseus molecular cloud, covering both a starless core and the protostellar core hosting the Class 0/I source IRAS 03445+3242. Using IRAM 30~m observations of N${}_2$H${}^{+}$(1--0), N${}_2$D${}^{+}$(1--0), H${}^{13}$CO${}^{+}$(1--0), and DCO${}^{+}$(2--1), complemented by C${}^{18}$O(2--1) data, we derive column density, deuterium fraction, and CO depletion maps. We find that the deuterium fraction in both mentioned nitrogen- and carbon-bearing species increases from the protostellar to the starless core, reaching $R_D^{{\mathrm{N}}_2{\mathrm{H}}^{+}}=0.43\pm 0.10$ and $R_D^{\mathrm{HC}{\mathrm{O}}^{+}}=0.09\pm 0.02$ in the starless core, compared with $0.15\pm 0.03$ and $0.05\pm 0.01$, respectively, in the protostellar core. The CO depletion factor also rises from $4.1\pm 0.1$ to $5.0\pm 0.1$ across the same transition. While the embedded YSO reduces deuteration in the dense inner gas, the less dense envelope traced by HCO${}^{+}$ is only slightly affected at our resolution. Our analysis confirms that CO freeze-out and the presence of a protostar jointly regulate deuterium chemistry in star-forming regions.

accepted for publication in ApJ

References in corpus (26)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Observing the gas temperature drop in the high-density nucleus of L 1544
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• The COMPLETE Survey of Star-Forming Regions: Phase I Data
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• Depletion and low gas temperature in the L183 prestellar core : the N2H+ - N2D+ tool
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• On the frequency of N2H+ and N2D+
• pyspeckit: A spectroscopic analysis and plotting package
• Benchmarking spin-state chemistry in starless core models
• The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out
• Carbon isotopic fractionation in molecular clouds
• Physical properties of the ambient medium and of dense cores in the Perseus star-forming region derived from Herschel Gould Belt Survey observations
• NH_3(1_0-0_0) in the pre-stellar core L1544
• A Survey of CH2DOH Towards Starless and Prestellar Cores in the Taurus Molecular Cloud
• A spider-like outflow in Barnard 5 - IRS 1: The transition from a collimated jet to a wide-angle outflow?
• Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves
• Methanol Mapping in Cold Cores: Testing Model Predictions
• Dissecting the super-critical filaments embedded in the 0.5 pc subsonic region of Barnard 5
• Combined model for ${}^{15}\mathrm{N}$, ${}^{13}\mathrm{C}$, and spin-state chemistry in molecular clouds
• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• Parsec-scale cosmic-ray ionisation rate in Orion
• Deuterium fractionation in cold dense cores in the low-mass star forming region L1688