Variable accretion and outflow in young brown dwarfs

We report on the first dedicated monitoring campaign of spectroscopic variability in young brown dwarfs. High-resolution optical spectra of six targets in nearby star-forming regions were obtained over 11 nights between 2005 January-March on the Magellan 6.5m telescope. We find significant variability in Halpha and a number of other emission lines related to accretion and outflow processes on a variety of timescales ranging from hours to weeks to years. The most dramatic changes are seen for 2M1207, 2M1101 and ChaI-ISO217. We observe possible accretion rate changes by about an order of magnitude in two of these objects, over timescales of weeks (2M1207) or hours (2M1101). The accretion 'burst' seen in 2M1101 could be due to a 'clumpy' flow. We also see indications for changes in the outflow rate in at least three objects. In one case (ISO217), there appears to be a ~1-hour time lag between outflow and accretion variations, consistent with a scenario in which the wind originates from the inner disk edge. Our variability study supports a close to edge-on inclination for the brown dwarf LS-RCrA 1. The fact that all targets in our sample show variations in accretion and/or outflow indicators suggests that studies of young brown dwarf properties should be based either on large samples or time series. As an example, we demonstrate that the large scatter in the recently found accretion rate vs. mass relationship can be explained primarily with variability. The observed profile variations imply asymmetric accretion flows in brown dwarfs, which, in turn, is evidence for magnetic funneling by large-scale fields. We show that accreting sub-stellar objects may harbor magnetic fields with ~kG strength (abridged).Comment: 33 pages, 5 figures, accepted for publication in Ap

The Herschel view of circumstellar discs: a multi-wavelength study of Chamaeleon I

We present the results of a multi-wavelength study of circumstellar discs around 44 young stellar objects in the 3 Myr old nearby Chamaeleon I star-forming region. In particular, we explore the far-infrared/submm regime using Herschel fluxes. We show that Herschel fluxes at 160-500$\,\mu$m can be used to derive robust estimates of the disc mass. The median disc mass is 0.005$M_{\odot}$ for a sample of 28 Class IIs and 0.006$M_{\odot}$ for 6 transition disks (TDs). The fraction of objects in Chamaeleon-I with at least the `minimum mass solar nebula' is 2-7%. This is consistent with previously published results for Taurus, IC348, $\rho$ Oph. Diagrams of spectral slopes show the effect of specific evolutionary processes in circumstellar discs. Class II objects show a wide scatter that can be explained by dust settling. We identify a continuous trend from Class II to TDs. Including Herschel fluxes in this type of analysis highlights the diversity of TDs. We find that TDs are not significantly different to Class II discs in terms of far-infrared luminosity, disc mass or degree of dust settling. This indicates that inner dust clearing occurs independently from other evolutionary processes in the discs.Comment: 16 pages, 13 figures. Accepted for publication in MNRA

Substellar Objects in Nearby Young Clusters (SONYC) IX: The planetary-mass domain of Chamaeleon-I and updated mass function in Lupus-3

Substellar Objects in Nearby Young Clusters -- SONYC -- is a survey program to investigate the frequency and properties of substellar objects in nearby star-forming regions. We present new spectroscopic follow-up of candidate members in Chamaeleon-I (~2 Myr, 160 pc) and Lupus 3 (~1 Myr, 200 pc), identified in our earlier works. We obtained 34 new spectra (1.5 - 2.4 mum, R~600), and identified two probable members in each of the two regions. These include a new probable brown dwarf in Lupus 3 (NIR spectral type M7.5 and Teff=2800 K), and an L3 (Teff=2200 K) brown dwarf in Cha-I, with the mass below the deuterium-burning limit. Spectroscopic follow-up of our photometric and proper motion candidates in Lupus 3 is almost complete (>90%), and we conclude that there are very few new substellar objects left to be found in this region, down to 0.01 - 0.02 MSun and Av \leq 5. The low-mass portion of the mass function in the two clusters can be expressed in the power-law form dN/dM \propto M^{-\alpha}, with \alpha~0.7, in agreement with surveys in other regions. In Lupus 3 we observe a possible flattening of the power-law IMF in the substellar regime: this region seems to produce fewer brown dwarfs relative to other clusters. The IMF in Cha-I shows a monotonic behavior across the deuterium-burning limit, consistent with the same power law extending down to 4 - 9 Jupiter masses. We estimate that objects below the deuterium-burning limit contribute of the order 5 - 15% to the total number of Cha-I members.Comment: Accepted for publication by Astrophysical Journa

CERTAIN PROBLEMS CONFRONTING CREDITORS WHEN A REVOCABLE TRUST ACCOMPLISHES TESTAMENTARY SUCCESSION

Under the overwhelming weight of authority the reservation by the settlor of the income from trust property, or of other benefits, during his lifetime, and of the power to revoke the trust and so recover all or any part of the principal does not invalidate the trust; nor does the trust fail because the trust instrument is not executed in accordance with the Statute of Wills. Upon the death of the settlor the corpus of such a trust is distributable by the trustee in accordance with the terms of the trust instrument and does not pass to the executor or administrator of the settlor

Applications of the Club Model to the Economics of Terrorism

Terrorism remains a controversial topic both in academia and in the public discourse. Building on previous social science research investigating the determinants of terrorism in a rational choice framework, I analyze terrorism through an economist\u27s lens that assumes terrorist groups to be rational actors that use violence as a tool in pursuit of tangible political or ideological goals. In the first chapter, I develop an economic model for the formation of alliances between terror groups, and why intergroup cooperation is more effective if the groups have a similar ideology. Groups cooperate in order to increase access to resources while maintaining the advantages of decentralization in the face of counterterrorism pressure. I empirically test the hypothesis that religious groups obtain greater operational benefits from cooperation than secular groups on a panel dataset containing detailed information on 255 terrorist groups between the years 1970 and 2014, finding that alliances formed by religious groups are more effective than those of their secular counterparts. In the second chapter, based on the so-called club model of terrorism, which postulates that terror groups may improve their capabilities by extracting sacrifices that screen out low commitment members and thus mitigating defection and free riding costs, I estimate the effects of these commitment devices on the incidence of terrorism. I do this by employing various observable proxies as exogenous shifters of the marginal product schedules of the ability of groups to induce commitment from members. Using a panel dataset containing all documented incidents of terror attacks from 2007–2013 at the state-year level, I find that the effects of the commitment devices are significant, both on overall terrorism and on suicide terrorism. The third chapter examines the relationship between party politics and terrorism. Combining economic theory with historical case studies of militant organizations in Lebanon, Turkey, Israel, Palestine, Spain, Ireland, and South America, I analyze the interplay between terrorism and party politics. Within a market framework that includes a supply side and a demand side, I describe how events affecting the marginal costs and marginal benefits of violence may induce an entry into, or exit from, terrorism

Development of a real-time aeroperformance analysis technique for the X-29A advanced technology demonstrator

The X-29A advanced technology demonstrator has shown the practicality and advantages of the capability to compute and display, in real time, aeroperformance flight results. This capability includes the calculation of the in-flight measured drag polar, lift curve, and aircraft specific excess power. From these elements many other types of aeroperformance measurements can be computed and analyzed. The technique can be used to give an immediate postmaneuver assessment of data quality and maneuver technique, thus increasing the productivity of a flight program. A key element of this new method was the concurrent development of a real-time in-flight net thrust algorithm, based on the simplified gross thrust method. This net thrust algorithm allows for the direct calculation of total aircraft drag

Emission Line Variability of the Accreting Young Brown Dwarf 2MASSW J1207334-393254: From Hours to Years

We have obtained a series of high-resolution optical spectra for the brown dwarf 2MASSW J1207334-393254 (2M1207) using the ESO Very Large Telescope with the UVES spectrograph during two consecutive observing nights (time resolution of ~12 min) and the Magellan Clay telescope with the MIKE spectrograph. Combined with previously published results, these data allow us to investigate changes in the emission line spectrum of 2M1207 on timescales of hours to years. Most of the emission line profiles of 2M1207 are broad, in particular that of Halpha, indicating that the dominant fraction of the emission must be attributed to disk accretion rather than to magnetic activity. From the Halpha 10% width we deduce a relatively stable accretion rate between 10^(-10.1...-9.8) Msun/yr for two nights of consecutive observations. Therefore, either the accretion stream is nearly homogeneous over (sub-)stellar longitude or the system is seen face-on. Small but significant variations are evident throughout our near-continuous observation, and they reach a maximum after ~8 h, roughly the timescale on which maximum variability is expected across the rotation cycle. Together with past measurements, we confirm that the accretion rate of 2M1207 varies by more than one order of magnitude on timescales of months to years. Such variable mass accretion yields a plausible explanation for the observed spread in the accretion rate vs. mass diagram. The magnetic field required to drive the funnel flow is on the order of a few hundred G. Despite the obvious presence of a magnetic field, no radio nor X-ray emission has been reported for 2M1207. Possibly strong accretion suppresses magnetic activity in brown dwarfs, similar to the findings for higher mass T Tauri stars.Comment: accepted for publication in Ap

Substellar Objects in Nearby Young Clusters (SONYC) VI: The planetary-mass domain of NGC1333

Within the SONYC - Substellar Objects in Nearby Young Clusters - survey, we investigate the frequency of free-floating planetary-mass objects (planemos) in the young cluster NGC1333. Building upon our extensive previous work, we present spectra for 12 of the faintest candidates from our deep multi-band imaging, plus seven random objects in the same fields, using MOIRCS on Subaru. We confirm seven new sources as young very low mass objects (VLMOs), with Teff of 2400-3100K and mid-M to early-L spectral types. These objects add to the growing census of VLMOs in NGC1333, now totaling 58. Three confirmed objects (one found in this study) have masses below 15 MJup, according to evolutionary models, thus are likely planemos. We estimate the total planemo population with 5-15 MJup in NGC1333 is <~8. The mass spectrum in this cluster is well approximated by dN/dM ~ M^-alpha, with a single value of alpha = 0.6+/-0.1 for M<0.6Msol, consistent with other nearby star forming regions, and requires alpha <~ 0.6 in the planemo domain. Our results in NGC1333, as well as findings in several other clusters by ourselves and others, confirm that the star formation process extends into the planetary-mass domain, at least down to 6 MJup. However, given that planemos are 20-50 times less numerous than stars, their contribution to the object number and mass budget in young clusters is negligible. Our findings disagree strongly with the recent claim from a microlensing study that free-floating planetary-mass objects are twice as common as stars - if the microlensing result is confirmed, those isolated Jupiter-mass objects must have a different origin from brown dwarfs and planemos observed in young clusters.Comment: 14 pages, 11 figures. Updated version after proof corrections, additional comment in Sect. 5.