2,160 research outputs found
The identification of 93 day periodic photometric variability for YSO YLW 16A
Aims. Periodic variability in young stellar objects (YSOs) offers indirect evidence for an active dynamical mechanism. Starspots, accretion, stellar companions, and disk veiling can contribute to the photometric variability of YSOs.
Methods. As part of an ongoing study of the Ï Oph star forming region, we report the discovery of 92.6 day periodic variations for the Class I YSO YLW 16A, observed over a period of three years. A SED model was fit to available photometric data for the object.
Results. We propose a triple-system with an inner binary with a period of 93 days eclipsed by a warped circum-binary disk. The nature of the secondary is unconstrained and could be stellar or sub-stellar. We confirm the discovery of a tertiary companion at a projected separation of ~40 AU that could account for the circum-binary disk warp. This light curve and model is similar to the model we proposed for WL 4 in previous work. Understanding these systems may lead to insights about the nature of stellar evolution and planetary formation, and provide valuable benchmarks for future theoretical modeling and near- and mid-infrared synoptic surveys of YSOs
The Nova Rate in M94 (NGC 4736)
A multi-epoch H survey of the early-type spiral galaxy M94 (NGC 4736)
has been completed as part of a program to establish the galaxy's nova rate. A
total of four nova candidates were discovered in seven epochs of observation
during the period from 2005 to 2007. After making corrections for temporal
coverage and spatial completeness, a global nova rate of 5.0
yr was determined. This rate corresponds to a specific-luminosity nova
rate of 1.4 0.5 novae per year per 10 when the
luminosity is determined from the color, or 1.5 0.4 novae per year
per 10 when the luminosity is derived from the Two
Micron All Sky Survey. These values are slightly lower than that of other
galaxies with measured nova rates, which typically lie in the range of
novae per year per 10 in the band.Comment: Accepted for publication in the Astrophysical Journal; 18 pages, 4
figures. The revised version includes a few stylistic changes and cleans up
some typo
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Community projects: an experimental analysis of a fair implementation process
We define and experimentally test a public provision mechanism that meets three basic ethical requirements and allows community members to influence, via monetary bids, which of several projects is implemented. For each project, participants are assigned personal values, which can be positive or negative. We provide either public or private information about personal values. This produces two distinct public provision games, which are experimentally implemented and analyzed for various projects. In spite of the complex experimental task, participants do not rely on bidding their own personal values as an obvious simple heuristic whose general acceptance would result in fair and efficient outcomes. Rather, they rely on strategic underbidding. Although underbidding is affected by projectsâ characteristics, the provision mechanism mostly leads to the implementation of the most efficient project
Photo-reverberation mapping of a protoplanetary accretion disk around a T Tauri star
This is the final version. Available from the American Astronomical Society via the DOI in this recordTheoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner "wall" at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the Ï Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 ÎŒm) and K (2.2 ÎŒm) bands were synchronized while the 4.5 ÎŒm emission lagged by 74.5 ± 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at âŒ1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.National Science Foundation (NSF
Incomplete Punishment Networks in Public Goods Games: Experimental Evidence
Abundant evidence suggests that high levels of contributions to public goods can be sustained through self-governed monitoring and sanctioning. This experimental study investigates the effectiveness of decentralized sanctioning institutions in alternative punishment networks. Our results show that the structure of punishment network significantly affects allocations to the public good. In addition, we observe that network configurations are more important than punishment capacities for the levels of public good provision, imposed sanctions and economic efficiency. Lastly, we show that targeted revenge is a major driver of anti-social punishment
Time-Resolved Photometry of the Optical Counterpart of Swift J2319.4+2619
Time-resolved CCD photometry is presented of the V~17 optical counterpart of
the newly-discovered, hard-X-ray-emitting polar Swift J2619.4+2619. A total of
~20 hr of data obtained over five nights in various bandpasses (B, V, R, and I)
reveals a strong quasi-sinusoidal modulation in the light curve at a
best-fitting period of 0.1254 d (3.01 hr), which we associate with the orbital
period of the system (one-day aliases of this period at 0.1114 d and 0.1435 d
are considered, but appear to be ruled out by our analysis). The amplitude of
the modulation increases with wavelength from ~0.8 mag in B to ~1.1 mag in R
and I. The increase in amplitude with wavelength is typical of polar systems
where the modulated radiation comes from cyclotron emission. The combination of
the relatively long orbital period and the emission of hard X-rays suggest that
Swift J2619.4+2619 may be a good candidate for an asynchronous polar system.Comment: 15 pages, 5 figures, Accepted for publication in the April 2008 PAS
Stated and revealed inequality aversion in three subject pools
This paper reports data from three subject pools (n=717 subjects) using techniques based on those of Loewenstein, et al. (1989) and Blanco, et al. (2011) to obtain parameters, respectively, of stated and revealed inequality aversion. We provide a replication opportunity for those papers, with two innovations: (i) a design which allows stated and revealed preferences to be compared at the individual level; (ii) assessment of robustness of findings across subjects from a UK university, a Turkish university and Amazon Mechanical Turk. Our findings on stated aversion to inequality are qualitatively similar to those of Loewenstein, et al. in each of our subject pools, whereas there are notable differences between some of our findings on revealed preference and those of Blanco, et al. We find that revealed advantageous inequality aversion is often stronger than revealed dis-advantageous inequality aversion. In most subject pools, we find some (weak) correlation between corresponding parameters of stated and revealed inequality aversion
The meaning of the virtual Midas touch: An ERP study in economic decision making
The Midas touch refers to the altruistic effects of a brief touch. Though these effects have often been replicated, they remain poorly understood. We investigate the psychophysiology of the effect using remotely transmitted, precisely timed, tactile messages in an economic decision-making game called Ultimatum. Participants were more likely to accept offers after receiving a remotely transmitted touch. Furthermore, we found distinct effects of touch on event-related potentials evoked by (a) feedback regarding accepted and rejected offers, (b) decision cues related to proposals, and (c) the haptic and auditory cues themselves. In each case, a late positive effect of touch was observed and related to the P3. Given the role of the P3 in memory-related functions, the results indicate an indirect relationship between touch and generosity that relies on memory. This hypothesis was further tested and confirmed in the positive effects of touch on later proposals
Asymmetric first-price auctions with uniform distributions: analytic solutions to the general case
While auction research, including asymmetric auctions, has grown significantly in recent years, there is still little analytical solutions of first-price auctions outside the symmetric case. Even in the uniform case, Griesmer et al. (1967) and Plum (1992) find solutions only to the case where the lower bounds of the two distributions are the same. We present the general analytical solutions to asymmetric auctions in the uniform case for two bidders, both with and without a minimum bid. We show that our solution is consistent with the previously known solutions of auctions with uniform distributions. Several interesting examples are presented including a class where the two bid functions are linear. We hope this result improves our understanding of auctions and provides a useful tool for future research in auctions
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