X-rays and Fluctuating X-Winds from Protostars

Shu, Frank H.; Shang, Hsien; Glassgold, A. E.; Lee, Typhoon

doi:10.1126/science.277.5331.1475

Cited by 384 publications

(285 citation statements)

References 38 publications

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“…Contributions to X-ray emission from star-disk interactions in general, and accretion in particular, decline as stars evolve from the T Tauri phase toward the main sequence. Such contributions may arise in star-disk magnetic field reconnection events (e.g., Shu et al 1997) or in energetic shocks along accretion columns (Kastner et al 2002). In either model, the emitting region temperature would be in excess of $10 6 K and therefore should contribute a relatively hard excess X-ray emission component that diminishes with age as the disk disperses.…”

Section: Discussionmentioning

confidence: 99%

ROSATX‐Ray Spectral Properties of Nearby Young Associations: TW Hydrae, Tucana‐Horologium, and the β Pictoris Moving Group

Kastner

Crigger

Rich

et al. 2003

ApJ

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We present archival ROSAT data for three recently identified, nearby (D < 70 pc), young ($10-40 Myr) stellar associations: the TW Hydrae association, the Tucana-Horologium association, and the Pictoris moving group. The distributions of ROSAT X-ray hardness ratios (HR1, HR2) for these three groups, whose membership is dominated by low-mass, weak-lined T Tauri stars, are tightly clustered and very similar to one another. The value of HR1 for TW Hya itself-the only bona fide classical T Tauri star in any of the nearby groups-is clearly anomalous among these nearby young stars. We compare the hardness ratio distributions of stars in the three nearby groups with those of T Tauri stars, the Hyades, and main-sequence dwarfs in the field. This comparison demonstrates that the X-ray spectra of F through M stars soften with age and that F and G stars evolve more rapidly in X-ray spectral hardness than do K and M stars. It is as yet unclear whether this trend can be attributed to age-dependent changes in the intrinsic X-ray spectra of stars of type F and later, to a decrease in the column density of circumstellar gas (e.g., in residual protoplanetary disks), or to the diminishing contributions of star-disk interactions to X-ray emission. Regardless, these results demonstrate that analysis of archival ROSAT X-ray spectral data can help both to identify nearby, young associations and to ascertain the X-ray emission properties of members of known associations.

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Section: Discussionmentioning

confidence: 99%

ROSATX‐Ray Spectral Properties of Nearby Young Associations: TW Hydrae, Tucana‐Horologium, and the β Pictoris Moving Group

Kastner

Crigger

Rich

et al. 2003

ApJ

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“…Scenarios with sharply-defined predictions would greatly aid in future work. Some significant efforts have been made in this direction since the work of Shu et al [263] [264]. However the physical plausibility of these models is not evident.…”

Section: Conclusion and Major Problems -Potential And Realmentioning

confidence: 99%

Short-lived nuclei in the early Solar System: Possible AGB sources

et al. 2006

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The abundances of short-lived radionuclides in the early solar system (ESS) are reviewed, as well as the methodology used in determining them. These results are compared with the inventory estimated for a uniform galactic production model. It is shown that, to within a factor of two, the observed abundances of 238 U, 235 U, 232 Th, 244 Pu, 182 Hf, 146 Sm, and 53 Mn are roughly compatible with long-term galactic nucleosynthesis. 129 I is an exception, with an ESS inventory much lower than expected from uniform production. The isotopes 107 Pd, 60 Fe, 41 Ca, 36 Cl, 26 Al, and 10 Be require late addition to the protosolar nebula. 10 Be is the product of energetic particle irradiation of the solar system as most probably is 36 Cl. Both of these nuclei appear to be present when 26 Al is absent. A late injection by a supernova (SN) cannot be responsible for most of the short-lived nuclei without excessively producing 53 Mn; it can however be the source of 53 Mn itself and possibly of 60 Fe. If a late SN injection is responsible for these two nuclei, then there remains the problem of the origin of 107 Pd and several other isotopes. Emphasis is given to an AGB star as a source of many of the nuclei, including 60 Fe; this possibility is explored with a new generation of stellar models. It is shown that if the dilution factor (i.e. the ratio of the contaminating mass to the solar parental cloud mass) is f 0 ∼ 4×10 −3 , a reasonable representation for many nuclei is obtained; this requires that ( 60 Fe/ 56 Fe) ESS ∼ 10 −7 to 2×10 −6 . The nuclei produced by an AGB source do not include 53 Mn, 10 Be or 36 Cl if it is very abundant. The role of irradiation is discussed with regard to 26 Al, 36 Cl and 41 Ca, and the estimates of bulk solar abundances of these isotopes are commented on. The conflict between various scenarios is emphasized as well as the current absence of an astrophysically plausible global interpretation for all the existing data. Examination of abundances for the actinides indicates that a quiescent interval of ∼ 10 8 years is required for actinide group production. This is needed in order to explain the data on 244 Pu and the new bounds on 247 Cm. Because this quiescent interval is not compatible with the 182 Hf data, a separate type of r-process event is needed for at least the actinides, distinct from the two types that have previously been identified. The apparent coincidence of the 129 I and trans-actinide time scales suggests that the last heavy r contribution was from an r-process that produced very heavy nuclei but without fission recycling so that the yields at Ba and below (including I) were governed by fission.

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“…Although it is well accepted that many high-energy processes in young stellar objects (YSOs) are dominated by magnetic activity (see Feigelson & Montmerle 1999 for a review) and that hard X-rays in flares are produced by powerful magnetic reconnections, star-disk activities, and jet formation, these findings are still confined to low-mass stars. In several models for Class I and II YSOs magnetic field play a crucial role in the X-ray production, in the form either of X-ray winds and accretion (Shu et al 1997) or of accretion shocks (Hartmann 1998). It has yet to be established how these models for low-mass YSOs may relate to more massive stars.…”

Section: Evolutionary Implicationsmentioning

confidence: 99%

X‐Ray Modeling of Very Young Early‐Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications

Schulz

Canizares

Huenemoerder

et al. 2003

ApJ

126

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The Orion Trapezium is one of the youngest and closest star-forming regions within our Galaxy. With a dynamic age of $3 Â 10 5 yr, it harbors a number of very young hot stars, which likely are on the zero-age main sequence (ZAMS). We analyzed high-resolution X-ray spectra in the wavelength range of 1.5-25 Å of three of its X-ray-brightest members (Â 1 Ori A, C, and E) obtained with the High Energy Transmission Grating Spectrometer (HETGS) on board the Chandra X-Ray Observatory. We measured X-ray emission lines, calculated differential emission measure distributions (DEMs), and fitted broadband models to the spectra. The spectra from all three stars are very rich in emission lines, specifically from highly ionized Fe, which includes emission from Fe xvii to Fe xxv ions. A complete line list is included. This is a mere effect of high temperatures rather than an overabundance of Fe, which in fact turns out to be underabundant in all three Trapezium members. Similarly there is a significant underabundance in Ne and O as well, whereas Mg, Si, S, Ar, and Ca appear close to solar. The DEM derived from over 80 emission lines in the spectrum of Â 1 Ori C indicates three peaks located at 7.9, 25, and 66 MK. The emission measure varies over the 15.4 day wind period of the star. For the two phases observed, the low-temperature emission remains stable, while the high-temperature emission shows significant differences. The line widths seem to show a similar bifurcation, where we resolve some of the soft X-ray lines with velocities up to 850 km s À1 (all widths are stated as halfwidth at half-maximum), whereas the bulk of the lines remain unresolved with a confidence limit of 110 km s À1 . The broadband spectra of the other two stars can be fitted with several collisionally ionized plasma model components within a temperature range of 4.3-46.8 MK for Â 1 Ori E and 4.8-42.7 MK for Â 1 Ori A. The high-temperature emissivity contributes over 70% to the total X-ray flux. None of the lines are resolved for Â 1 Ori A and E with a confidence limit of 160 km s À1 . The influence of the strong UV radiation field on the forbidden line in the He-like triplets allows us to set an upper limit on distance of the line-emitting region from the photosphere. The bulk of the X-ray emission cannot be produced by shock instabilities in a radiation-driven wind and are likely the result of magnetic confinement in all three stars. Although confinement models cannot explain all the results, the resemblance of the unresolved lines and of the DEM with recent observations of active coronae in II Peg and AR Lac during flares is quite obvious. Thus we speculate that the X-ray production mechanism in these stars is similar, with the difference that the Orion stars may be in a state of almost continuous flaring driven by the wind. We clearly rule out major effects due to X-rays from a possible companion. The fact that all three stars appear to be magnetic and are near zero age on the main sequence also raises the issue of whether the Orion stars are ...

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X-rays and Fluctuating X-Winds from Protostars

Cited by 384 publications

References 38 publications

ROSATX‐Ray Spectral Properties of Nearby Young Associations: TW Hydrae, Tucana‐Horologium, and the β Pictoris Moving Group

ROSATX‐Ray Spectral Properties of Nearby Young Associations: TW Hydrae, Tucana‐Horologium, and the β Pictoris Moving Group

Short-lived nuclei in the early Solar System: Possible AGB sources

X‐Ray Modeling of Very Young Early‐Type Stars in the Orion Trapezium: Signatures of Magnetically Confined Plasmas and Evolutionary Implications

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