Betelgeuse’s Buddy: X-Ray Constraints on the Nature of α Ori B

We present 12CO and 13CO molecular gas data observed by ALMA, massive early-stage young stellar objects (YSOs) identified by applying color–magnitude cuts to Spitzer and Herschel photometry, and low-mass late-stage YSOs identified via excess. Using dendrograms, we derive properties for the molecular cloud structures. This is the first time a dendrogram analysis has been applied to extragalactic clouds. The majority of clumps have a virial parameter equal to unity or less. The size–linewidth relations of 12CO and 13CO show the clumps in this study have a larger linewidth for a given size (by factors of 3.8 and 2.5, respectively) in comparison to several, but not all, previous studies. The larger linewidths in 30 Doradus compared to typical Milky Way quiescent clumps are probably due to the former’s highly energetic environmental conditions. The slopes of the size–linewidth relations of 12CO, 0.65 ± 0.04, and 13CO, 0.97 ± 0.12, are on the higher end but consistent within 3σ of those of previous studies. Massive star formation occurs in clumps with high masses (>1.83 × 102 M ⊙), high linewidths (v > 1.18 km s−1), and high mass densities (>6.67 × 102 M ⊙ pc−2). The majority of embedded, massive YSOs are associated with a clump; however, the majority of more evolved, low-mass YSOs are not.

Asymptotic giant branch stars (AGBs) and young stellar objects (YSOs) often share the same domains in infrared (IR) color–magnitude or color–color diagrams leading to potential misclassification. We extracted a list of AGB interlopers from the published YSO catalogs using the periodogram analysis on the Near-Earth Object Wide Infrared Survey Explorer (NEOWISE) time series data. YSO IR variability is typically stochastic and linked to episodic mass accretion. Furthermore, most variable YSOs are at an early evolutionary stage, with significant surrounding envelope and/or disk material. In contrast, AGBs are often identified by a well-defined sinusoidal variability with periods of a few hundreds days. From our periodogram analysis of all known low-mass YSOs in the Gould Belt, we find 85 AGB candidates, out of which 62 were previously classified as late-stage Class III YSOs. Most of these new AGB candidates have similar IR colors to O-rich AGBs. We observed 73 of these AGB candidates in the H2O, CH3OH, and SiO maser lines to further reveal their nature. The SiO maser emission was detected in 10 sources, confirming them as AGBs because low-mass YSOs, especially Class III YSOs, do not show such maser emission. The H2O and CH3OH maser lines were detected in none of our targets.

We have developed a Monte Carlo code for the transport of stellar X-rays in an axially symmetric disk. The code treats Compton scattering and photoelectric absorption and follows the X-rays until they are completely absorbed. We confirm that hard X-rays from a low-mass young stellar object (YSO) penetrate the associated accretion disk. Even without the low-energy photons that are strongly attenuated by the YSO wind, the ionization rate in the inner region of the accretion disk (<1 AU) is many orders of magnitude larger than the standard ionization rate due to Galactic cosmic rays. At a fixed radius from the source, the X-ray ionization rate is a universal function of the vertical column density, independent of the structural details of the disk. The ionization rate scales with the X-ray luminosity and depends only mildly on the X-ray temperature, at least for the temperatures relevant for low-mass YSOs. Thus X-rays from a YSO can ionize regions of an accretion disk from which low-energy cosmic rays are excluded, e.g., by the action of stellar winds. Using a simple theory for the electron fraction we estimate that, for a minimum solar nebula, X-rays ionize the disk beyond 5 AU at a level sufficient to couple magnetic fields and neutral disk material. Inside this radius, the X-rays are ineffective for vertical column densities much larger than ~1025 cm-2, and thus an interior region of the disk will be uncoupled from magnetic fields. If disk accretion is mediated by MHD turbulence, as proposed by Balbus & Hawley, then our results suggest that layered accretion occurs in the inner regions of a disk ionized by X-rays, in accord with Gammie's suggestion based on cosmic-ray ionization.

Numerous studies on hydrodynamics of the Keplerian as well as the sub-Keplerian accretion disk around a compact object (e.g., white dwarf (WD), neutron star (NS), or a black hole) have attempted to explain the observed UV, soft, and hard X-ray spectra. Although, when the compact object (e.g., a WD or an NS) has a finite surface, its rapid rotation, the stellar magnetic field could cause deformation of the spherical symmetry. Earlier studies on the Keplerian disk showed that a deviation from the spherical symmetry of the compact object could affect the observed light curve and spectra at high frequencies. Here, we have explored the effect of the nonspherical nature of a compact object on the hydrodynamics of an optically thin, geometrically thick sub-Keplerian advective flow. We find that due to the nonspherical shape of the central accretor, there is a possibility to trigger Rankine–Hugoniot shock in the sub-Keplerian advective flow close to the accretor without considering any general relativistic effect or presence of the hard surface of the star. Our results are more relevant for accretion onto a WD as hardly any general relativistic effect will come into the picture. We propose that some observational features, e.g., high significance of fitting the spectra with multi-temperature plasma models rather than single-temperature models, and variable efficiency of X-ray emission (X-ray luminosity in comparison with the optical and UV luminosity of the disk) in nonmagnetic cataclysmic variables can be explained by the presence of a shock in the sub-Keplerian advective flow.

We report multi-epoch Very Long Baseline Interferometry (VLBI) H2O maser observations towards the compact cluster of young stellar objects (YSOs) close to the Herbig Be star LkHα 234. This cluster includes LkHα 234 and at least nine more YSOs that are formed within projected distances of ∼10 arcsec (∼9000 au). We detect H2O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact (∼0.2 arcsec = ∼180 au), bipolar H2O maser outflow emerging from the embedded YSO Very Large Array (VLA) 2. We estimate a kinematic age of ∼40 yr for this bipolar outflow, with expanding velocities of ∼20 km s−1 and momentum rate ṀwVw ≃ 10−4–10−3 M⊙ yr−1 km s−1 × (Ω/4π), powered by a YSO of a few solar masses. We propose that the outflow is produced by recurrent episodic jet ejections associated with the formation of this YSO. Short-lived episodic ejection events have previously been found towards high-mass YSOs. We show now that this behaviour is also present in intermediate-mass YSOs. These short-lived episodic ejections are probably related to episodic increases in the accretion rate, as observed in low-mass YSOs. We predict the presence of an accretion disc associated with VLA 2. If detected, this would represent one of the few known examples of intermediate-mass stars with a disc–YSO–jet system at scales of a few hundred astronomical units.

Disc and sphere dust models are used to fit 8‐13 µm flux spectra of 19 low-mass young stellar objects (YSOs) and five Herbig AeBe stars. The 13 non-photospheric low-mass YSOs in quiescent environments and the five Herbig AeBe stars have mean disc temperature indices of 0.4, indicating that the emission arises from optically thin layers above a flared optically thick disc; 10 out of 14 of the low-mass YSO and four out of five of the Herbig AeBe features contain an optically thin silicate emission component. The radius of the peak 10-µm emission for nine out of the 13 low-mass YSOs is 10‐130 au, and three out of the five Herbig AeBe stars are 10‐30 au in size. In contrast, the five YSOs from disrupted molecular clouds that have been shaped by expanding supernova remnants have temperature indices of between 0.3 and 0.8; four out of the five are optically thick and three out of the five have radii 2 au. The photosphere-like continuum of Taurus-Elias 18 could be fitted only with truncated optically thick models, implying the presence of a void between the >500 K and cold (100 K) foreground dust. Silicates surrounding low-mass YSOs in quiescent molecular clouds are similar to those in the Trapezium region of the Orion Nebula except when AV 2 mag. In the low-AV case and in low-mass YSOs in disrupted molecular clouds the silicates are similar to circumstellar dust around the evolved star µ Cephei.

The low-mass star formation region associated with the reflection nebula Cederblad 110 in the Chamaeleon I cloud was mapped with the Australian Telescope Compact Array (ATCA) at 6 and 3.5 cm. Altogether 11 sources were detected, three of which are previously known low mass young stellar objects associated with the nebula: the illuminating star IRS 2 (Class III, Einstein X-ray source CHX 7), the brightest far-infrared source IRS 4 (Class I), and the weak X-ray source CHX10a (Class III). The other young stellar objects in the region, including the Class 0 protostar candidate Cha-MMS1, were not detected. The radio spectral index of IRS 4 (= 1:7 0:3) is consistent with optically thick free-free emission arising from a dense ionized region, probably a jet-induced shock occurring in the circumstellar material. As the only Class I protostar with a thermal jet IRS 4 is the strongest candidate for the central source of the molecular outflow found previously in the region. The emission from IRS 2 has a flat spectrum ( = 0:05 0:05) but shows no sign of polarization, and therefore its origin is likely to be optically thin free-free emission either from ionized wind or a collimated jet. The strongest source detected in this survey is a new compact object with a steep negative spectral index ( 1:1) and a weak linear polarization (2%), which probably represents a background radio galaxy.

The low-mass star formation region associated with the reflection nebula Cederblad 110 in the Chamaeleon I cloud was mapped with the Australian Telescope Compact Array (ATCA) at 6 and 3.5cm. Altogether 11 sources were detected, three of which are previously known low mass young stellar objects associated with the nebula: the illuminating star IRS2 (Class III, Einstein X-ray source CHX7), the brightest far-infrared source IRS4 (Class I), and the weak X-ray source CHX10a (Class III). The other young stellar objects in the region, including the Class 0 protostar candidate Cha-MMS1, were not detected. The radio spectral index of IRS4 (alpha = 1.7 +/- 0.3) is consistent with optically thick free-free emission arising from a dense ionized region, probably a jet-induced shock occurring in the circumstellar material. As the only Class I protostar with a 'thermal jet' IRS4 is the strongest candidate for the central source of the molecular outflow found previously in the region. The emission from IRS2 has a flat spectrum (alpha = 0.05 +/- 0.05) but shows no sign of polarization, and therefore its origin is likely to be optically thin free-free emission either from ionized wind or a collimated jet. The strongest source detected in this survey is a new compact object with a steep negative spectral index (-1.1) and a weak linear polarization (about 2 %), which probably represents a background radio galaxy.

We explore the X-ray properties of the young stellar and substellar objects in the open cluster IC 348 as seen in our deep Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer image. First, we give identifications of all X-ray sources and determine upper limits for the X-ray luminosities of the undetected cluster members. Then we analyze the X-ray spectra of the young stellar objects, deriving plasma temperatures between ~0.7 and ~3 keV for the T Tauri stars in IC 348 and higher temperatures, between ~3 and ~7 keV, for flaring sources and two embedded young stellar objects. We find several large X-ray flares, in some of which a clear hardening of the X-ray spectra during the flare peak is seen. Next we use the exceptional optical, infrared, and X-ray data set of this cluster to study various correlations and their implications, and to discuss new answers to some long-standing questions related to X-ray emission from young (sub)stellar objects. The X-ray luminosities of the young low-mass stars are strongly correlated to the stellar bolometric luminosities (LX ~ 10-4 × Lbol). Also, a good correlation between X-ray luminosity and stellar mass is found (LX ∝ M2). For the weak-line T Tauri stars we find a tight correlation between X-ray activity and chromospheric activity (LX ∝ L), supporting the hypothesis that the chromosphere is heated by X-rays from the overlying corona. The observed X-ray properties of the brown dwarfs (and brown dwarf candidates) are very similar to those of late-type stars; we explain this behavior as the consequence of the fact that very young substellar objects are still warm enough to maintain partially ionized atmospheres, which are capable of sustaining electrical currents, while in the cooler neutral atmospheres of L and T dwarfs such currents are shut off (hence no X-ray emission). Finally, we explore the difference between the X-ray luminosity functions of classical and weak-line T Tauri stars. We find that the classical T Tauri stars in IC 348 seem to be on average less X-ray luminous than the weak-line T Tauri stars. However, we suggest that this apparent difference is caused by a selection effect: there is a strong detections bias against those weak-line T Tauri stars that are optically faint and hence X-ray faint; the population of classical T Tauri stars, on the other hand, is essentially completely known because of its very prominent Hα emission. This conclusion is corroborated by another new result: when using a photometrically selected, magnitude-limited, complete sample of T Tauri stars and taking the K-L infrared excess as a tracer of circumstellar material, we find no evidence in IC 348 for a difference in X-ray properties of young stars with and without circumstellar matter, i.e., classical and naked T Tauri stars.

Massive young stellar objects (YSOs), like low-mass YSOs, are thought to be surrounded by optically thick envelopes and/or discs and are observed to have associated regions that produce polarized light at near-infrared wavelengths. These polarized regions are thought to be lower density outflows along the polar axes of the YSO envelopes. Using the 0.2 arcsec spatial resolution of Near-Infrared Camera and Multi-Object Spectrometer on the Hubble Space Telescope, we are examining the structure of the envelopes and outflow regions of massive YSOs in star-forming regions within a few kpc of the Sun. Here, we report on 2 μm polarimetry of Mon R2-IRS3, S140-IRS1 and AFGL 2591. All three sources contain YSOs with highly polarized monopolar outflows, with Mon R2-IRS3 containing at least two YSOs in a small cluster. The central stars of all four YSOs are also polarized, with position angles perpendicular to the directions of the outflows. We infer that this polarization is due to scattering and absorption by aligned grains. We have modelled our observations of S140-IRS1 and AFGL 2591 as light scattered and absorbed both by spherical grains and by elongated grains that are aligned by magnetic fields. Models that best reproduce the observations have a substantial toroidal component to the magnetic field in the equatorial plane. Moreover, the toroidal magnetic field in the model that best fits AFGL 2591 extends a large fraction of the height of the model cavity, which is 105 au. We conclude that the massive YSOs in this study all show evidence of the presence of a substantial toroidal magnetic field.

Winds of high-mass main sequence and highly evolved stars are probably driven primarily by radiation pressure acting on the wind gas (e.g. Lucy and Abbot 1993), while the sustained winds of low-mass and intermediate-ma1;1s highly evolved stars may be affected substantially by radiation pressure acting on dust (cf. Chapter 12). However, radiation pressure is incapable of inducing the high mass-loss rates of 10-9 M0 yr-1 to 10-4 M0 yr-1 characteristic of low-mass (;≲ 4 M0) young stellar objects (YSOs) in some phases of their evolution. The highest mass-loss rates are often associated with clearly defined bipolar flows (e.g. Bachiller 1996); some low-mass YSOs are also seen to possess jets and Herbig-Haro objects (cf. Chapter 10).

We report the results of a search for 6.7 GHz methanol masers toward low-mass young stellar objects (YSOs) and (pre)protostellar condensations with the Australia Telescope Compact Array (ATCA). Our sample consisted of 13 class 0 proto- stars and 44 class I YSOs as well as 66 (pre)protostellar condensations. A single detection was obtained toward NGC 2024: FIR4 in the Orion B region. This is the first detection of a 6.7 GHz methanol maser in Orion. The nature of FIR4 has been a subject of debate with some evidence suggesting that it is a very cold high-mass (pre)protostellar condensation and others arguing that it is a low-mass YSO. The discovery of a methanol maser associated with this source is inconsistent with both of these hypotheses and we suggest that FIR4 probably harbours an intermediate- or high-mass YSO. The less massive objects in our sample do not exhibit any methanol maser stronger than 400 mJy (4). Based on the nil detection rate toward the low-mass YSOs we can place an upper limit of 3 10 6 K on the brightness temperature of any methanol maser associated with class 0, I or II sources. These results support the hypothesis that no strong methanol masers are associated with low-mass star formation (<3 M).

This paper presents a statistical study in which the observed total luminosity is compared quantitatively with an estimate of the stellar luminosity for a sample of 59 low-mass young stellar objects (YSOs) in the Taurus-Auriga complex. In 13 of the analyzed YSOs, luminosity excesses greater than 0.20 are observed together with greater than 0.6 IR excesses, which typically contribute the bulk of the observed excess luminosity and are characterized by spectral energy distributions which are flat or rise toward long wavelengths. The analysis suggests that YSOs showing the largest luminosity excesses typically power optical jets and/or molecular outflows or have strong winds, as evidenced by the presence of O I emission, indicating a possible correlation between accretion and mass-outflow properties. 38 references.

After a critical overview of the generalized uncertainty principle (GUP) applied to compact objects, we propose a texture of Heisenberg uncertainty principle in curved spacetimes (CHUP). CHUP allows to write down physically motivated STUR (spacetime uncertainty relations) in a generic background for a non commutative spacetime in terms of tetrad variables. In order to study possible quantum effects for compact astrophysical objects as white dwarf, neutron stars and black holes, an expression for quantum fluctuations is outlined. As a result, contrary to GUP-based claims, we found no evidence for quantum effects concerning equilibrium equation and critical mass M c for white dwarf and neutron stars. Conversely, our expression for CHUP confirms that general relativistic effects strongly reduce the Oppenheimer–Volkoff Newtonian limit for very compact astrophysical objects as neutron stars. In particular, we found that for a degenerate relativistic Fermi gas, the maximum mass decreases for increasing compactness of the star with a minimum critical mass M c ≃ 0.59M ⊙ at the Buchdahl limit. Finally, we study possible non commutative effects near the event horizon of a black hole.

view Abstract Citations (19) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Nature of the X-Ray Pulsar near Lynds 1457 Patterson, J. ; Halpern, J. P. Abstract The rotation of a magnetized white dwarf or neutron star accidentally located within or behind the Lynds 1457 molecular cloud, is considered as a model for the hard X-ray source H0253 + 193. It is calculated that all models of this type have a low a priori probability because the positions are so remarkably coincident and because the objects involved are not sufficiently common. A neutron star accreting in a close binary is rejected because its likelihood is extremely small and because the observed position, luminosity, and spectrum of the object are all quite atypical for X-ray binaries. Two other possibilities are considered: (1) an isolated white dwarf or neutron star drifting accidentally into the cloud and accreting sufficient gas to power the X-ray source and (2) a white dwarf accreting in a close binary. Publication: The Astrophysical Journal Pub Date: September 1990 DOI: 10.1086/169180 Bibcode: 1990ApJ...361..173P Keywords: Astronomical Models; Molecular Clouds; Pulsars; X Ray Binaries; Cataclysmic Variables; Magnetic Stars; Neutron Stars; Stellar Rotation; White Dwarf Stars; Astrophysics; NEBULAE: INDIVIDUAL ALPHANUMERIC: L1457 (LYNDS 1457); PULSARS; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (12)