[Paper Review] TIMASSS: The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey. I. Observations, calibration and analysis of the line kinematics

E. Caux, C. Kahane+16 more|University of Groningen research database (University of Groningen / Centre for Information Technology)|Mar 28, 2011

Astrophysics and Star Formation StudiesPhysics and Astronomy114 references85 citations

TL;DR

This paper presents the TIMASSS spectral survey of the solar-type protostar IRAS16293-2422, using the IRAM 30 m and JCMT 15 m telescopes to conduct a comprehensive millimeter and submillimeter line survey. It detects over 4,000 lines across 200 GHz, identifies 70 species, and reveals two distinct velocity components in the binary system, with source A showing increasing line widths at higher energy transitions consistent with gas infall toward a ~1 M⊙ object, while source B exhibits no such trend, suggesting a much lower mass (~0.1 M⊙).

ABSTRACT

While unbiased surveys observable from ground-based telescopes have previously been obtained towards several high mass protostars, very little exists on low mass protostars. To fill up this gap, we carried out a complete spectral survey of the bands at 3, 2, 1 and 0.8 mm towards the solar type protostar IRAS16293-2422. The observations covered about 200\,GHz and were obtained with the IRAM-30m and JCMT-15m telescopes. Particular attention was devoted to the inter-calibration of the obtained spectra with previous observations. All the lines detected with more than 3 sigma and free from obvious blending effects were fitted with Gaussians to estimate their basic kinematic properties. More than 4000 lines were detected (with sigma \geq 3) and identified, yielding a line density of approximatively 20 lines per GHz, comparable to previous surveys in massive hot cores. The vast majority (~2/3) of the lines are weak and due to complex organic molecules. The analysis of the profiles of more than 1000 lines belonging 70 species firmly establishes the presence of two distinct velocity components, associated with the two objects, A and B, forming the IRAS16293-2422 binary system. In the source A, the line widths of several species increase with the upper level energy of the transition, a behavior compatible with gas infalling towards a ~1 Mo object. The source B, which does not show this effect, might have a much lower central mass of ~0.1 Mo. The difference in the rest velocities of both objects is consistent with the hypothesis that the source B rotates around the source A. This spectral survey, although obtained with single-dish telescope with a low spatial resolution, allows to separate the emission from 2 different components, thanks to the large number of lines detected. The data of the survey are public and can be retrieved on the web site http://www-laog.obs.ujf-grenoble.fr/heberges/timasss.

Motivation & Objective

• To conduct a complete, unbiased millimeter and submillimeter spectral survey of the low-mass protostar IRAS16293-2422, a solar-type protostellar system.
• To address the lack of comprehensive spectral surveys toward low-mass protostars compared to high-mass hot cores.
• To analyze the kinematic structure of the source using a large number of detected molecular lines to disentangle emission from the binary components A and B.
• To determine the physical conditions and dynamical state of the gas in the two components, particularly testing for infall signatures in source A.
• To provide a publicly accessible, high-resolution spectral line database for future astrochemical and physical studies of low-mass star formation.

Proposed method

• Conducted a 200 GHz spectral survey using the IRAM 30 m and JCMT 15 m telescopes, accumulating ~300 hours of integration time.
• Performed rigorous inter-calibration of data between the two telescopes to ensure spectral consistency and flux accuracy.
• Identified all emission lines with signal-to-noise ratio ≥3 and minimal blending, using the CASSIS and GILDAS-CLASS software packages.
• Fitted detected lines with Gaussian profiles to derive kinematic parameters including line center frequency, full width at half maximum (FWHM), and integrated flux.
• Analyzed the dependence of line width on upper-level energy to infer dynamical processes such as infall or rotation.
• Used the rest frequency and velocity offset of lines to distinguish emission from the two components, A and B, in the binary system.

Experimental results

Research questions

• RQ1 What is the molecular line content and kinematic structure of the low-mass protostar IRAS16293-2422 across 3, 2, 1, and 0.8 mm bands?
• RQ2 Can the spectral survey resolve the emission from the two components (A and B) in the binary system based on line kinematics?
• RQ3 Is there evidence of gas infall in source A, indicated by increasing line widths with increasing upper-level energy of transitions?
• RQ4 What are the dynamical masses implied by the kinematic behavior of the two components?
• RQ5 How do the physical conditions and molecular excitation differ between source A and source B?

Key findings

• The survey detected 4,037 lines with signal-to-noise ≥3, yielding a line density of approximately 20 lines per GHz, comparable to massive hot cores.
• Approximately two-thirds of the detected lines originate from complex organic molecules, highlighting the rich chemistry in low-mass protostars.
• The kinematic analysis of over 1,000 lines from 70 species revealed two distinct velocity components, corresponding to the binary components A and B.
• In source A, the line widths increase with the upper-level energy of the transitions, a signature consistent with gas infall toward a central mass of ~1 M⊙.
• In source B, no such trend is observed, suggesting a much lower central mass of ~0.1 M⊙, consistent with a lower-mass object or a more quiescent environment.
• The velocity offset between the two components is consistent with source B orbiting source A, supporting a binary system configuration.