18,748 research outputs found
Bananas About Brown Dwarfs
No full textThe astroquarks are joined by Dr. Adam Burgasser from the Cool Star Lab at the University of California San Diego to talk about the mysterious members of the astrophysical menagerie that lie between planets and stars. Brown dwarfs are lurking in the dark, sometimes closer than we might think. We also have spaceflight history trivia, 20 new moons, and a spot about G
ADAM SMITH'S OPTIMISTIC TELEOLOGICAL VIEW OF HISTORY
No full textAdam Smith's four-stage theory provides the framework for his writings on history. The fourth stage is the commercial epoch; the culmination of history in this stage is a key component in the conventional interpretation of Adam Smith as a prophet of commercialism. In two historical case studies Smith shows the capacity of commercial society to regenerate itself. This potent capacity suggests that commercial society is inevitable. At a certain point in time it also overcomes the major obstacles to its permanence. Smith's philosophy of history anticipates the end of history views of Kant and Hegel.Political Economy,
How Might Adam Smith Pay Professors Today?
No full textAdam Smith’s proposal for paying professors was intended to induce increased faculty knowledge. If students have imperfect information about what they learn, and universities can only imperfectly measure the input of faculty time in student learning, publications may be used to measure faculty knowledge. If professors’ ability to publish is positively related to their ability to produce student learning, which universities can imperfectly measure, publications may be necessary to attract more able professors. Since research signals faculty knowledge, schools that do not value publications per se could require higher publication standards and pay higher wages than schools that value only publications.
ADAM SMITH'S VIEW OF HISTORY: CONSISTENT OR PARADOXICAL?
No full textThe conventional interpretation of Adam Smith is that he is a prophet of commercialism. The liberal capitalist reading of Smith is consistent with the view that history culminates in commercial society. The first part of the article develops this optimistic interpretation of Smith's view of history. Smith implies that commercial society is the end of history because 1) it supplies the ends of nature that he identifies; 2) it is inevitable; and 3) it is permanent. The second part of the article shows that Smith has some dark moments in his writings where he seems to reject completely such teleological notions. In this more civic humanist mood he confesses that commercial society does not supply the ends of nature, nor is it inevitable, nor is it permanent. Both views exist in Smith and the commentator is forced to choose between passages in Smith's work in order to support a particular interpretation of the former's view of history.Political Economy,
2MASS J20261584–2943124: AN UNRESOLVED L0.5 + T6 SPECTRAL BINARY
No full textWe identify the L dwarf 2MASS J20261584–2943124 as an unresolved spectral binary, based on low-resolution, near-infrared spectroscopy from IRTF/SpeX. The data reveal a peculiar absorption feature at 1.6 μm, previously noted in the spectra of other very low-mass spectral binaries, which likely arises from overlapping FeH and CH[subscript 4] absorption bands in the blended light of an L dwarf/T dwarf pair. Spectral template matching analysis indicates component types of L0.5 and T6, with relative brightness ΔH = 4.2 ± 0.6. Laser guide star adaptive optics imaging observations with Keck/NIRC2 fail to resolve the source, indicating a maximum separation at the observing epoch of 0['' over .]25, or a projected separation of 9 AU assuming a distance of 36 ± 5 pc. With an age that is likely to be relatively older ([> over ~]5 Gyr) based on the system's large V [subscript tan] and mass ratio arguments, the relative motion of the potentially "massive" (0.06-0.08 M [subscript ☉]) components of 2MASS J2026–2943 may be detectable through radial velocity variations, like its earlier-type counterpart 2MASS J03202839–0446358 (M8+T5), providing dynamical mass measurements that span the hydrogen burning limit
THE SURFACE COMPOSITION OF LARGE KUIPER BELT OBJECT 2007 OR10
No full textWe present photometry and spectra of the large Kuiper belt object 2007 OR10. The data show significant near-infrared absorption features due to water ice. While most objects in the Kuiper belt with water ice absorption this prominent have the optically neutral colors of water ice, 2007 OR10 is among the reddest Kuiper belt objects known. One other large Kuiper belt object—Quaoar—has similar red coloring and water ice absorption, and it is hypothesized that the red coloration of this object is due to irradiation of the small amounts of methane able to be retained on Quaoar. 2007 OR10, though warmer than Quaoar, is in a similar volatile retention regime because it is sufficiently larger that its stronger gravity can still retain methane. We propose, therefore, that the red coloration on 2007 OR10 is also caused by the retention of small amounts of methane. Positive detection of methane on 2007 OR10 will require spectra with higher signal to noise. Models for volatile retention on Kuiper belt objects appear to continue to do an excellent job reproducing all of the available observations
The Brown Dwarf Kinematics Project
No full textBrown dwarfs are a recent addition to the plethora of objects studied in Astronomy. With theoretical masses between 13 and 75 MJupiter, they lack sustained stable Hydrogen burning so they never join the stellar main sequence. They have physical properties similar to both planets and low--mass stars so studies of their population inform on both. The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet, until my thesis, fundamental measurements of parallax and proper motion were made for only a relatively small fraction of the known population. To address this deficiency, I initiated the Brown Dwarf Kinematics (BDKP). Over the past four years I have re-imaged the majority of spectroscopically confirmed field brown dwarfs (or ultracool dwarfs--UCDs) and created the largest proper motion catalog for ultracool dwarfs to date. Using new astrometric information I examined population characteristics such as ages calculated from velocity dispersions and correlations between kinematics and colors. Using proper motions, I identified several new wide co-moving companions and investigated binding energy (and hence formation) limitations as well as the frequency of hierarchical companions. Concurrently over the past four years I have been conducting a parallax survey of 84 UCDs including those showing spectral signatures of youth, metal-poor brown dwarfs, and those within 20 pc of the Sun. Using absolute magnitude relations in J,H, and K, I identified overluminous binary candidates and investigated known flux-reversal binaries. Using current evolutionary models, I compared the MK vs J-K color magnitude diagram to model predictions and found that the low-surface gravity dwarfs are significantly redward and underluminous of predictions and a handful of late-type T dwarfs may require thicker clouds to account for their scatter.Advisor(s): Frederick M. Walter. Adam J. Burgasser. Committee Member(s): Michael M. Shara; Michael Zingale; Anand Sivaramakrishnan; Dan Davis.Stony Brook University Libraries. SBU Graduate School in Department of Physics. Lawrence Martin (Dean of Graduate School)
ULAS J141623.94+134836.3: A BLUE T DWARF COMPANION TO A BLUE L DWARF
No full textWe confirm the substellar nature of ULAS J141623.94+134836.3 (aka SDSS J1416+1348B), a common proper motion companion to the blue L dwarf SDSS J141624.08+134826.7 identified by Burningham et al. and Scholz. Low-resolution 0.8-2.4 μm spectroscopy obtained with the Infrared Telescope Facility/SpeX shows strong H[subscript 2]O and CH[subscript 4] absorption bands, consistent with a T7.5 spectral type, and we see possible indications of NH[subscript 3] absorption in the 1.0-1.3 μm region. More importantly, the spectrum of SDSS J1416+1348B shows a broadened Y-band peak and highly suppressed K-band flux, both indicative of high surface gravity and/or subsolar metallicity. These traits are verified through spectral model fits, from which we derive atmospheric parameters T [subscript eff] = 650 ± 60 K, log g = 5.2 ± 0.4 cgs, [M/H] ≤ –0.3, and K[subscript zz] = 10[superscript 4] cm[superscript 2] s[superscript –1], the temperature being significantly warmer than that estimated by Burningham et al. These fits also indicate a model-dependent spectroscopic distance of 10.6[+3.0 over –2.8] pc for SDSS J1416+1348B, formally consistent with the 7.9 ± 1.7 pc astrometric distance for SDSS J1416+1348A from Scholz. The common peculiarities of these two co-spatial, co-moving sources suggest that their unusual blue colors—and those of other blue L and T dwarfs in general—arise from age/gravity or metallicity effects, rather than cloud properties alone
AN AGE CONSTRAINT FOR THE VERY LOW MASS STELLAR/BROWN DWARF BINARY 2MASS J03202839-0446358AB
No full text2MASS J03202839–0446358AB is a recently identified, late-type M dwarf/T dwarf spectroscopic binary system for which both the radial velocity orbit for the primary and spectral types for both components have been determined. By combining these measurements with predictions from four different sets of evolutionary models, we determine a minimum age of 2.0 ± 0.3 Gyr for this system, corresponding to minimum primary and secondary masses of 0.080 M sun and 0.053 M sun, respectively. We find broad agreement in the inferred age and mass constraints between the evolutionary models, including those that incorporate atmospheric condensate grain opacity; however, we are not able to independently assess their accuracy. The inferred minimum age agrees with the kinematics and absence of magnetic activity in this system, but not the rapid rotation of its primary, further evidence of a breakdown in angular momentum evolution trends amongst the lowest luminosity stars. Assuming a maximum age of 10 Gyr, we constrain the orbital inclination of this system to i gsim 53°. More precise constraints on the orbital inclination and/or component masses of 2MASS 0320–0446AB, through either measurement of the secondary radial velocity orbit (optimally in the 1.2-1.3 μm band) or detection of an eclipse (only 0.3% probability based on geometric constraints), would yield a bounded age estimate for this system, and the opportunity to use it as an empirical test for brown dwarf evolutionary models at late ages
OPTICAL AND NEAR-INFRARED SPECTROSCOPY OF THE L SUBDWARF SDSS J125637.13-022452.4
No full textRed optical and near-infrared spectroscopy are presented for SDSS J125637.13-022452.4, one of only four L subdwarfs reported to date. These data confirm the low-temperature, metal-poor nature of this source, as indicated by prominent metal-hydride bands, alkali lines, and collision-induced H2 absorption. The optical and near-infrared spectra of SDSS J1256-0224 are similar to those of the sdL4 2MASS J16262034+3925190, and we derive a classification of sdL3.5 based on the preliminary scheme of Burgasser, Cruz, and Kirkpatrick. The kinematics of SDSS J1256-0224 are consistent with membership in the Galactic inner halo, with estimated UVW space velocities indicating a slightly prograde, eccentric, and inclined Galactic orbit (3.5 lsim R lsim 11 kpc; |Zmax| = 7.5 kpc). Comparison to synthetic spectra computed with the PHOENIX code, including the recent implementation of kinetic condensate formation (DRIFT-PHOENIX), indicates T eff ≈ 2100-2500 K and [M/H] ≈ –1.5 to –1.0 for log g ≈ 5.0-5.5 (cgs), although there are clear discrepancies between model and observed spectra particularly in the red optical region. As such, any conclusions on the role of metallicity in condensate grain and cloud formation are probably premature. Indeed, a shift in the temperature scale of L subdwarfs relative to L dwarfs may obviate the need for modified condensate and grain chemistry in low metallicity atmospheres
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