No Transition Disk? Infrared Excess, PAH, H-2, And X-Rays From The Weak-Lined T Tauri Star DoAr 21

As part of a program to understand disk dispersal and the interplay between circumstellar disks and X-ray emission, we present new high-resolution mid-infrared (IR) imaging, high-resolution optical spectroscopy, and Chandra grating X-ray spectroscopy of the weak-lined T Tauri star DoAr 21. DoAr 21 (age \u3c 10(6) yr and mass similar to 2.2M(circle dot) based on evolutionary tracks) is a strong X-ray emitter, with conflicting evidence in the literature about its disk properties. It shows weak but broad H alpha emission (reported here for the first time since the 1950s); polarimetric variability; polycyclic aromatic hydrocarbon (PAH) and H-2 emission; and a strong, spatially resolved 24 mu m excess in archival Spitzer photometry. Gemini sub-arcsecond-resolution 9-18 mu m images show that there is little or no excess mid-IR emission within 100 AU of the star; the excess emission is extended over several arcseconds and is quite asymmetric. The extended emission is bright in the ultraviolet (UV)-excited lambda = 11.3 mu m PAH emission feature. A new high-resolution X-ray grating spectrum from Chandra shows that the stellar X-ray emission is very hard and dominated by continuum emission; it is well fit by a multi-temperature thermal model, typical of hard coronal sources, and shows no evidence of unusually high densities. A flare during the X-ray observation shows a temperature approaching 10(8) K. We argue that the far-UV emission from the transition region is sufficient to excite the observed extended PAH and continuum emission, and that the H-2 emission may be similarly extended and excited. While this extended emission may be a disk in the final stages of clearing, it also could be more akin to a small-scale photodissociation region than a protoplanetary disk, highlighting both the very young ages (\u3c10(6) yr) at which some stars are found without disks and the extreme radiation environment around even late-type pre-main-sequence stars

Do CEOs Exercise Their Stock Options Earlier than Other Executives?

This paper looks at the timing chosen by CEOs to exercise their stock options and to sell their shares of stock compared to the timing chosen by other top executives in the firm. We first present a model that predicts when CEOs should exercise their options and/or sell their shares, and when other top managers should. Using a tournament approach we find that other top executives should exercise their stock options later than the CEO. We test this model using an unique data set of Canadian companies from 1993 onward. Our results seem to support the theoretical model as non-CEO executives seem to exercise their stock options about a calendar year later than the CEO. Moreover, non-CEO executive a more likely to exercise when a new CEO has been appointed, confirming our tournament model results. Nous étudions dans cet article le moment choisi par le PDG d'une compagnie pour lever ses options ou vendre ses actions dans la compagnie comparativement au moment choisi par les autres hauts dirigeants de la compagnie. Nous présentons premièrement un modèle théorique de tournoi qui fait des prédictions quant au moment opportun pour le PDG et les autres dirigeants de lever leurs options et/ou de vendre leurs actions dans la compagnie. Nous montrons théoriquement dans un tel modèle de tournoi que les hauts dirigeants devraient lever leurs options après le PDG. Nous testons ce modèle en utilisant une base de données unique de compagnies canadiennes de 1993 à 1999. Nos résultats empiriques semblent supporter notre modèle théorique puisque les hauts dirigeants semblent lever leurs options un an plus tard que le PDG. De plus, les hauts dirigeants semblent plus enclins à lever leurs options lorsqu'un nouveau PDG vient d'être nommé, confirmant ainsi notre modèle de tournoi.CEO and Executive Compensation, Options, Timing of Exercised Options., Contributions volontaires, pertes publiques, risque, ambiguïté, données expérimentales

Diagnostics Of Disks Around Hot Stars

We discuss three different observational diagnostics related to disks around hot stars: absorption line determinations of rotational velocities of Be stars; polarization diagnostics of circumstellar disks; and X-ray line diagnostics of one specific magnetized hot star, theta(1) Ori C. Some common themes that emerge from these studies include (a) the benefits of having a specific physical model as a framework for interpreting diagnostic data; (b) the importance of combining several different types of observational diagnostics of the same objects; and (c) that while there is often the need to reinterpret traditional diagnostics in light of new theoretical advances, there are many new and powerful diagnostics that are, or will soon be, available for the study of disks around hot stars

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

Radiative Corrections in a Vector-Tensor Model

In a recently proposed model in which a vector non-Abelian gauge field interacts with an antisymmetric tensor field, it has been shown that the tensor field possesses no physical degrees of freedom. This formal demonstration is tested by computing the one-loop contributions of the tensor field to the self-energy of the vector field. It is shown that despite the large number of Feynman diagrams in which the tensor field contributes, the sum of these diagrams vanishes, confirming that it is not physical. Furthermore, if the tensor field were to couple with a spinor field, it is shown at one-loop order that the spinor self-energy is not renormalizable, and hence this coupling must be excluded. In principle though, this tensor field does couple to the gravitational field

Improving Reactions to Forced-Choice Personality Measures in Simulated Job Application Contexts Through the Satisfaction of Psychological Needs

There is a wealth of evidence justifying the use of personality assessments for selection. Nonetheless, some reluctance to use these assessments stems from their perceived vulnerability to response distortion (i.e., faking) and the somewhat negative applicant reactions they elicit, when compared to other assessments. Adopting a forced-choice personality assessment format appears to alleviate the former problem but exacerbates the latter. In this study, we introduce basic psychological needs as a theoretical foundation to develop interventions to improve reactions to forced-choice personality assessments. We propose that the forced-choice format impedes respondents’ desire to respond to items in a preferred way, interfering with autonomy need satisfaction, and constrains respondents’ opportunity to show their capabilities, interfering with competence need satisfaction. In this pre-registered between-subjects experiment (N = 1565), we investigated two modifications to a ranked forced-choice personality questionnaire and compared these to traditional forced-choice and single-stimulus (Likert) formatted questionnaires. One modification, where participants could write a free-text response following the assessment, did not show significant effects on reactions. The second modification allowed participants to view all items they had ranked last (first) and then identify any the participant believed in fact described them well (poorly). That modification positively affected perceived autonomy- and competence-support, and fairness perceptions, bridging approximately half of the gap between reactions to forced-choice and single-stimulus assessment formats. This study suggests that a modification to forced-choice personality questionnaires may improve applicant reactions and that basic psychological needs theory may be a fruitful lens through which to further understand reactions to assessments