Star Formation In Taurus Research Articles

Multiplicity and clustering in Taurus star forming region

Context. Multiplicity and clustering of young pre-main sequence stars appear as critical clues to understand and constrain the star formation process. Taurus is the archetypical example of the most quiescent star forming regions that may still retain primeval signatures of star formation. Aims. This work identifies local overdense stellar structures as a critical scale between wide pairs and loose groups in Taurus. Methods. Using the density-based spatial clustering of applications with noise (dbscan) algorithm, and setting its free parameters based on the one-point correlation function and the k-nearest neighbor statistics, we have extracted reliably overdense structures from the sky-projected spatial distribution of stars. Results. Nearly half of the entire stellar population in Taurus is found to be concentrated in 20 very dense, tiny and prolate regions called NESTs (for Nested Elementary STructures). They are regularly spaced (≈2 pc) and mainly oriented along the principal gas filaments axes. Each NEST contains between four and 23 stars. Inside NESTs, the surface density of stars may be as high as 2500 pc−2 and the mean value is 340 pc−2. Nearly half (11) of these NESTs contain about 75% of the class 0 and I objects. The balance between Class I, II, and, III fraction within the NESTs suggests that they may be ordered as an evolutionary temporal scheme, some of them getting infertile with time, while other still giving birth to young stars. We have inferred that only 20% of stars in Taurus do not belong to any kind of stellar groups (either multiple system, ultra wide pairs or NESTs). The mass-size relation for stellar NESTs is very close to the Bonnor–Ebert expectation. The range in mass is about the same as that of dense molecular cores. The distribution in size is bimodal peaking at 12.5 and 50 kAU and the distribution of the number of YSOs in NESTs as a function of size exhibits two regimes. Conclusions. We propose that the NESTs in their two size regimes represent the spatial imprints of stellar distribution at birth as they may have emerged within few millions years from their natal cloud either from a single core or from a chain of cores. We have identified them as the preferred sites of star formation in Taurus. These NESTs are the regions of highest stellar density and intermediate spatial scale structures between ultra-wide pairs and loose groups.

MASSES AND DISTANCE OF THE YOUNG BINARY NTTS 045251+3016

As part of our continuing campaign to measure the masses of pre-main sequence stars dynamically and thus to assess the reliability of the discrepant theoretical calculations of contraction to the main sequence, we present new results for NTTS 045251+3016, a visual and double-lined spectroscopic binary in the Taurus Star Forming Region. We obtained new high angular resolution astrometry and high spectral resolution spectroscopy at Keck Observatory. The new data lead to a significant revision of previously published orbital parameters. In particular, we find that the masses of the primary and secondary are 0.86+/-0.11 and 0.55+/-0.05 M_sun, respectively, smaller than previously reported, and that the system lies 158.7+/-3.9 pc from the sun, further than previously reported.

Tidal forces as a regulator of star formation in Taurus

Only a few molecular clouds in the solar neighbourhood exhibit the formation of only low-mass stars. Traditionally, these clouds have been assumed to be supported against more vigorous collapse by magnetic fields. The existence of strong magnetic fields in molecular clouds, however, poses serious problems for the formation of stars and of the clouds themselves. In this Letter, we review the three-dimensional structure and kinematics of Taurus – the archetype of a region forming only low-mass stars – as well as its orientation within the Milky Way. We conclude that the particularly low star formation efficiency in Taurus may naturally be explained by tidal forces from the Galaxy, with no need for magnetic regulation or stellar feedback.

Cavities in inner disks: the GM Aurigae case

Context. Recent modeling based on unresolved infrared observations of the spectral energy distribution (SED) of GM Aurigae suggests that the inner disk of this single TTauri star is truncated at an inner radius of 25 AU. Aims. We attempt to find evidence of this inner hole in the gas distribution, using spectroscopy with high angular resolution. Methods. Using the IRAM array, we obtained high angular resolution (∼1.5) observations with a high S/N per channel of the 13 CO J = 2-1 and C 18 O J = 2-1 and of the 13 CO J = 1-0 lines. A standard parametric disk model is used to fit the line data in the Fourier-plane and to derive the CO disk properties. Our measurement is based on a detailed analysis of the spectroscopic profile from the CO disk rotating in Keplerian velocity. The millimeter continuum, tracing the dust, is also analyzed. Results. We detect an inner cavity of radius 19±4 AU at the 4.5σ- level. The hole manifests itself by a lack of emission beyond the (projected) Keplerian speed at the inner radius. We also constrain the temperature gradient in the disk. Conclusions. Our data reveal the existence of an inner hole in GM Aur gas disk. Its origin remains unclear, but can be linked to planet formation or to a low mass stellar companion orbiting close to the central star (∼5-15 AU). The frequent finding of inner cavities suggests that either binarity is the most common scenario of star formation in Taurus or that giant planet formation starts early.

Comments on Inferences of Star Formation Histories and Birth Lines

Palla & Stahler have recently argued that star formation in Taurus and other nearby molecular clouds extends over a period of at least 10 Myr, implying quasi-static cloud evolution and star formation. Their conclusions contradict other recent results indicating that molecular clouds are transient objects and star formation proceeds rapidly. The Palla & Stahler picture implies that most molecular clouds should have extremely low rates of star formation and that in such inactive stages, the stellar initial mass function (IMF) should be strongly skewed toward producing stars with masses 1 M☉; neither prediction is supported by observations. I show that the Palla & Stahler conclusions for Taurus depend almost entirely on a small number of stars with masses 1 M☉; the lower mass stars show no evidence for such an extended period of star formation. I further show that most of the stars apparently older than 10 Myr in the direction of Taurus are probably foreground nonmembers. I also present birth line calculations that support the idea that the ages of the stars with masses 1 M☉ have been systematically overestimated because birth line age corrections have been underestimated; such birth lines would eliminate the need to postulate skewed IMFs. The simplest and most robust explanation of current observations characterizing the vast majority of young stars in molecular clouds is that cloud and star formation is rapid and dynamic.

A high-resolution radio survey of Class I protostars

We report the results of a survey of low mass Class I protostars in the cm continuum. In the initial survey, seven sources in the Taurus star formation were observed with the VLA at 0``.25 resolution. All seven sources drive CO outflows and display Herbig-Haro flows in the optical or near infrared wavebands. 4/7 sources were detected, two of which are new discoveries in systems of very low luminosity, one being the lowest luminosity system detected to date in the cm continuum. Notably, three sources were not detected to a 3-sigma limit of 0.10 mJy/beam, which indicates that significant cm continuum emission is not a universal feature of Class I systems with outflow activity. Subsequent observations of HH30, a more evolved Class II system, found no emission to a 3-sigma limit of 0.03 mJy/beam. After comparison with near infrared data, we suggest that the discriminating feature of the detected systems is a relatively high ionisation fraction in the stellar wind. Temporal variability of the outflow may also play a role. The one relatively bright source, IRAS 04016+2610 (L1489 IRS), is clearly resolved on a 0``.4 scale at 2 cm and 3.5 cm. Follow-up imaging with MERLIN did not detect this source with a 0``.04 beam, indicating that the radio emission is generated in a region with a radius of about 25 au, which is broadly similar to the radius of the bipolar cavities inferred from models of near infrared data. Interpretation of this system is complicated by the existence of a quadrupolar outflow, which we originally detected through polarimetric imaging. We present a near infrared H2 image in which a bow shock in the secondary outflow is clearly seen. This complicated structure may have been caused by a gravitational interaction between two protostars.

A Large-Scale Objective-Prism and X-Ray Survey in Taurus-Auriga

We present the results of a moderately deep, wide-field optical/X-ray survey extending over ~60° in the Taurus-Auriga molecular cloud complex. Our observations are sensitive enough to allow us to detect lower mass and older pre–main-sequence stars that could have been missed in previous surveys. We identify four new T Tauri stars, two in the area of L1500 and L1503, one in L1538, and one in L1544. X-rays were detected from three near-IR sources, one of them a very reddened Class II T Tauri star. Four X-ray sources have no known optical/IR known counterpart; they could be very reddened pre–main-sequence stars. Our findings are consistent with the idea that little (if any) star formation has taken place in L1537 and L1538. Although we found one slightly older T Tauri star (~3–4 Myr old), our survey yields no evidence for any significant number of T Tauri stars, regardless of mass and age, outside the main groups of young stars in Taurus. We conclude that the M stars comprising the low-mass end of the ROSAT All-Sky Survey (RASS) source population must be older than ~10 Myr and most probably unrelated to the ongoing process of star formation in Taurus. Instead, the bulk of the RASS sources seen toward regions like Taurus seem to trace the history of star formation over a longer period in the solar vicinity.

Star formation in taurus

Data with the 2MASS prototype camera were obtained in a 2.3 sq. deg region in Taurus containing Heiles Cloud 2, a region known from IRAS observations to contain a number of very young solar type stars.

Global aspects of dynamics and star formation in Taurus

We employ a number of data sets that include the proper motions of T-Tauri stars, molecular and H I velocities and densities, optical polarimetry, and H-alpha-luminosities of young stars in order to derive a global view of gas dynamics and star formation in the Taurus molecular cloud. We find strong correlations among cloud properties. TTS stars move in a direction that is roughly parallel to the gaseous filaments in the cloud. Assuming that stars and gas are well coupled, we infer that the cloud moves through the ISM at approximately 17 km s-1. The Taurus cloud is a member of Gould's Belt, and it is moving in the same direction as the other members. We propose that the cloud's motion arises as a consequence of its formation through Parker instability in the ISM. The bulk of gas displaced by this instability moves laterally at several times the Alfven speed of the undisturbed gas as it falls back toward the galaxy. It is this motion that is consistent with that of Taurus. An odd (antisymmetric with respect to reflection through the Galactic plane) mode Parker instability produces a warped gas layer which we interpret to be the origin of Gould's Belt, of which Taurus is a small constituent. The infalling gas will shock with material in the plane of the Belt. MHD waves are generated in this process, and we suggest that this is the origin of large-scale Alfven waves in Taurus. Such waves do not damp for the life of the cloud and keep it supported against global gravitational collapse. The gravitational energy release during the Parker instability is sufficient to account for the kinematics of the cloud as well as its internal stirring. The motion of the Taurus cloud is mildly super-Alfvenic with respect to the surrounding undisturbed WNM, and this must be associated with a shock. There are indications of the presence of a shock of speed V(sh) congruent-to 6.7 km s-1 in Taurus. This shock is suggested to be responsible of the relative velocity drift of 3.8 km s-1 between the weaker H I self-absorption component and the rest of the cloud (CO, H I emission, PMS stars). Observational support for the existence of a large-scale Alfven wave in Taurus comes from both the wavelike distortion of the cloud magnetic field (wavelength of 17 pc) and the wavelike disturbance in the velocity field of this H I component which matches up with the magnetic data. Finally, the influence of the shock in the star formation process is analyzed. It is shown that there are no significant differences in the evolutionary state of groups of PMS stars located at very different positions in the cloud. It appears as if many features of the dynamics and physics of the cloud are determined by global issues such as the process of cloud formation and its interaction with the larger scale ISM.

Global properties of star formation in Taurus

A careful analysis of the data available in the literature has been carried out to determine the global properties of star formation in Taurus. Three main trends arise in the data: (1)the magnetic field in Taurus is distorted in the direction of the proper motions of the T Tauri Stars (TIS) (see below).(2)the groups with different proper motions seem to have different stellar contents. An analysis of the stellar population based on the equivalent width of Hα, W(Hα), shows that groups I and III (Jones and Herbig, 1979) have approximately the same population (TTS show either large or small W(Hα)). However in group II (central part of the cloud) there are also a large number of stars with intermediate W(Hα) (Gomez de Castro and Pudritz, 1990).(3)the mass function of the NH3 cores (thought to be "protostellar cores") is dN/dM< M∝ with α=−1.5, in contrast with the IMF of the TTS given by Cohen and Kuhi (1979), α=−2.5. Only point (1) will be outlined in this contribution.

Global properties of star formation in Taurus

A careful analysis of the data available in the literature has been carried out to determine the global properties of star formation in Taurus. Three main trends arise in the data: (1)the magnetic field in Taurus is distorted in the direction of the proper motions of the T Tauri Stars (TIS) (see below).(2)the groups with different proper motions seem to have different stellar contents. An analysis of the stellar population based on the equivalent width of Hα, W(Hα), shows that groups I and III (Jones and Herbig, 1979) have approximately the same population (TTS show either large or small W(Hα)). However in group II (central part of the cloud) there are also a large number of stars with intermediate W(Hα) (Gomez de Castro and Pudritz, 1990).(3)the mass function of the NH3 cores (thought to be "protostellar cores") is dN/dM< M∝ with α=−1.5, in contrast with the IMF of the TTS given by Cohen and Kuhi (1979), α=−2.5. Only point (1) will be outlined in this contribution.

Wave dynamics and star formation in Taurus

The mechanism underlying the formation of cores and larger scale structures in molecular clouds must play a fundamental role in the physics of star formation since young stellar objects are usually found within or very near cores (Myers et al 1987, Beichman et al 1986). The Taurus cloud is an ideal object to study in this regard because of its proximity (160 pc), and because only low mass star formation is presently occurring there. Barnard's (1927) beautiful optical photograph of the region reveals that the obscuring gas and dust has filamentary structure that is comparable to the size of the cloud complex (several 10's of pc). This structure is clearly seen in CO maps of the region as well (eg. Duvert et al 1986) where it is apparent that structure on much larger size scales than cores is common. In addition to the filamentary structure one also observes that there are small dark clouds present such as L1489, L1495, etc.

Wave dynamics and star formation in Taurus

The mechanism underlying the formation of cores and larger scale structures in molecular clouds must play a fundamental role in the physics of star formation since young stellar objects are usually found within or very near cores (Myers et al 1987, Beichman et al 1986). The Taurus cloud is an ideal object to study in this regard because of its proximity (160 pc), and because only low mass star formation is presently occurring there. Barnard's (1927) beautiful optical photograph of the region reveals that the obscuring gas and dust has filamentary structure that is comparable to the size of the cloud complex (several 10's of pc). This structure is clearly seen in CO maps of the region as well (eg. Duvert et al 1986) where it is apparent that structure on much larger size scales than cores is common. In addition to the filamentary structure one also observes that there are small dark clouds present such as L1489, L1495, etc.

Star Formation in Taurus, the IRAS View

In the course of its short existence the IRAS database has already proved an incredibly powerful tool for studying the classification of sources -both galactic and extragalactic- in a new and very exciting way. For the first time it is now possible to employ selection criteria based purely on the infrared properties of a complete (to very low intensities) and unbiassed infrared sample - thereby eliminating the selection biases which have critically limited any such previous classifications.

X-ray sources in regions of star formation. I - The naked T Tauri stars

view Abstract Citations (192) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Sources in Regions of Star Formation. I. The Naked T Tauri Stars Walter, F. M. Abstract Einstein X-ray observations of regions of active star formation in Taurus, Ophiuchus, and Corona Australis show a greatly enhanced surface density of stellar X-ray sources over that seen in other parts of the sky. Many of the X-ray sources are identified with low-mass, pre-main-sequence stars which are not classical T Tauri stars. The X-ray, photometric, and spectroscopic data for these stars are discussed. Seven early K stars in Oph and CrA are likely to be 1-solar-mass post-T Tauri stars with ages of 10-million yr. The late K stars in Taurus are not post-T Tauri, but 'naked' T Tauri stars, which are coeval with the T Tauri stars, differing mainly in the lack of a circumstellar envelope. Publication: The Astrophysical Journal Pub Date: July 1986 DOI: 10.1086/164367 Bibcode: 1986ApJ...306..573W Keywords: Pre-Main Sequence Stars; Star Formation; T Tauri Stars; X Ray Sources; Astronomical Photometry; Chromosphere; Early Stars; K Stars; Main Sequence Stars; Space Density; Stellar Evolution; Stellar Spectra; Astrophysics; STARS: PRE--MAIN-SEQUENCE; X-RAYS: SOURCES full text sources ADS | data products SIMBAD (38) NED (1) MAST (1) Related Materials (5) Part 2: 1987ApJ...314..297W Part 3: 1988AJ.....96..297W Part 4: 1992AJ....104..758W Part 5: 1994AJ....107..692W Part 6: 1997AJ....114.1544W