Molecular line study of the very young protostar IRAM 04191 in Taurus: Infall, rotation, and outflow

By A.Belloche, P.Andre, D.Despois, S. d'Astrophysique, O. Bordeaux, Division of Hospital, H. Center. 2002

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We present a detailed millimeter line study of the circumstellar environment of the low-luminosity Class 0 protostar IRAM 04191+1522 in the Taurus molecular cloud. New line observations demonstrate that the ~14000 AU radius protostellar envelope is undergoing both extended infall and fast, differential rotation. Radiative transfer modeling of multitransition CS and C34S maps indicate an infall velocity v_inf ~ 0.15 km/s at r ~ 1500 AU and v_inf ~ 0.1 km/s up to r ~ 11000 AU, as well as a rotational angular velocity Omega ~ 3.9 x 10^{-13} rad/s, strongly decreasing with radius beyond 3500 AU down to a value Omega ~ 1.5-3 x 10^{-14} rad/s at ~ 11000 AU. Two distinct regions, which differ in both their infall and their rotation properties, therefore seem to stand out: the inner part of the envelope (r ~< 2000-4000 AU) is rapidly collapsing and rotating, while the outer part undergoes only moderate infall/contraction and slower rotation. These contrasted features suggest that angular momentum is conserved in the collapsing inner region but efficiently dissipated due to magnetic braking in the slowly contracting outer region. We propose that the inner envelope is in the process of decoupling from the ambient cloud and corresponds to the effective mass reservoir (~0.5 M_sun) from which the central star is being built. Comparison with the rotational properties of other objects in Taurus suggests that IRAM 04191 is at a pivotal stage between a prestellar regime of constant angular velocity enforced by magnetic braking and a dynamical, protostellar regime of nearly conserved angular momentum. The rotation velocity profile we derive for the inner IRAM 04191 envelope should thus set some constraints on the distribution of angular momentum on the scale of the outer Solar system at the onset of protostar/disk formation.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/d662290c7854b14a37d94bae5a91e1427cf71a05

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Citations in the corpus

Ambipolar diffusion in low-mass star formation - I. General comparison with the ideal magnetohydrodynamic case (2015, background): “Even though a Bonnor-Ebert (BE) density profile may better fit observations of dense cores (see Andre et al. 2000; Belloche et al. 2002) and has an analytical foundation (Li & Shu 1996; Hunter 1977), we assumed a magnetised medium permeated by straight parallel field lines, and it is hardly…”
Collapse of Magnetized Singular Isothermal Toroids. II. Rotation and Magnetic Braking (2003, background): “The best studied circumstellar structure of this type is perhaps the one around the source IRAM 04191 (Belloche et al. 2002), which we discuss in some depth below.”
Disk formation during collapse of magnetized protostellar cores (2009, background): “However, because of difficulties in disentangling the emission of the disk and envelope, the existence of disks around class 0 objects remains a matter of debate (Mundy et al. 2000, Belloche et al. 2002, Jorgensen et al. 2007).”
Probing the formation of intermediate- to high-mass stars in protoclusters - A detailed millimeter study of the NGC 2264 clumps (2005, methodology): “Moreover, the rotational curve expected from differential rotation is characterized by a continuous ”S” shape (cf. Belloche et al. 2002) rather than a sharp velocity discontinuity as observed here.”
Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores (2007, background): “IRAM 04191 drives a large, bipolar molecular outflow, features bright molecular line and dust continuum emission, and shows evidence for infall, depletion, and deuteration (André et al. 1999; Belloche et al. 2002).”
Evolution of Chemistry and Molecular Line Profiles during Protostellar Collapse (2004, background): “…important physical parameter to constrain theoretical models in star formation, can only be obtained from molecular spectra (Mizuno et al. 1990; Zhou et al. 1993; Choi et al. 1995; Gregersen et al. 1997; Mardones et al. 1997; Gregersen et al. 1998; Di Francesco et al. 2001; Belloche et al. 2002).”
Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit (2007, background): “Molecular line observations have established that the envelope is both infalling and differentially rotating (Belloche et al. 2002).”
Magnetic processes in a collapsing dense core I. Accretion and ejection (2007, background): “In the fifth part, we qualitatively compare our results with various observations, focussing particularly on the young class 0 source, IRAM04191 (André et al. 1999, Belloche et al. 2002) The sixth part concludes the paper.”
The initial conditions of star formation in the Ophiuchus main cloud: Kinematics of the protocluster condensations , (2007, unknown): “3.3 of Belloche et al. 2002).”
The physics of star formation (2003, background): “Observations of collapsing cloud cores confirm that angular momentum is approximately conserved on scales smaller than a few hundredths of a parsec (Ohashi et al 1997; Ohashi 1999; Myers et al 2000; Belloche et al 2002).”
High- and Low-Velocity Magnetized Outflows in the Star Formation Process in a Gravitationally Collapsing Cloud (2008, background): “Molecular outflows observed by CO line emission exhibit awide opening angle (e.g., Belloche et al. 2002) and slower velocity (10Y50 km s 1; Richer et al. 2000; Arce et al. 2007), while optical jets observed by optical emission exhibit good collimation and higher velocity (100Y500 km; Bally et al.…”
Observing the gas temperature drop in the high-density nucleus of L 1544 (2007, result): “…velocity resolution should be needed to confirm this loss of specific angular momentum towards the small scales; however, this differential rotational properties between the inner envelopes and the ambient cloud is consistent with other observations in more evolved objects (Belloche et al. 2002).”
Protostellar disk formation and transport of angular momentum during magnetized core collapse (2012, background): “The density profile of the initial cloud ρ = ρ0 1 + (r/r0)2 , where ρ0 is the central density and r0 the initial radius of the spherical cloud is in accordance with observations (André et al. 2000; Belloche et al. 2002).”