I. Neill Reid

Space Telescope Science Institute, Baltimore, Maryland, United States

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Publications (261)814.27 Total impact

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    ABSTRACT: The binary brown dwarf WISE J104915.57$-$531906.1 (also Luhman 16AB), composed of a late L and early T dwarf, is a prototypical L/T transition flux reversal binary located at only 2 pc distance. Luhman 16B is a known variable whose light curves evolve rapidly. We present spatially resolved spectroscopic time-series of Luhman 16A and B covering 6.5 h using HST/WFC3 at 1.1 to 1.66 $\mu$m. The small, count-dependent variability of Luhman 16A at the beginning of the observations likely stems from instrumental systematics; Luhman 16A appears non-variable above $\approx$0.4%. Its spectrum is well fit by a single cloud layer with intermediate cloud thickness (f_sed=2, Teff=1200 K). Luhman 16B varies at all wavelengths with peak-to-valley amplitudes of 7-11%. The amplitude and light curve shape changes over only one rotation period. The lowest relative amplitude is found in the deep water absorption band at 1.4 $\mu$m, otherwise it mostly decreases gradually from the blue to the red edge of the spectrum. This is very similar to the other two known highly variable early T dwarfs. A two-component cloud model accounts for most of the variability, although small deviations are seen in the water absorption band. We fit the mean spectrum and relative amplitudes with a linear combination of two models of a warm, thinner cloud (Teff=1300 K, fsed=3) and a cooler, thicker cloud (Teff=1000-1100 K, f_sed=1), assuming out-of-equilibrium atmospheric chemistry. A cloud as for Luhman 16A but with holes cannot reproduce the variability of Luhman 16B, indicating more complex cloud evolution through the L/T transition. The projected separation of the binary has decreased by $\approx$0.3'' in 8 months.
    The Astrophysical Journal 10/2014; 798(2). DOI:10.1088/0004-637X/798/2/127 · 6.28 Impact Factor
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    I. Neill Reid
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    ABSTRACT: Proposal success rates are calculated for HST Cycles 11 through 21 as a function of the gender of the Principal Investigator (PI). In each cycle, proposals with male PIs have a higher success rate, with the disparity greatest for Cycles 12 and 18. The offsets are small enough that they might be ascribed to chance for any single cycle, but the consistent pattern suggests the presence of a systematic effect. Closer inspection of results from Cycles 19, 20 and 21 shows that the systematic difference does not appear to depend on the geographic origin of the proposal nor does it depend on the gender distribution on the review panels. Segregating proposals by the seniority of the PI, the success rates by gender for more recent graduates (Ph.d. since 2000) are more closely comparable. There is also a correlation between success by gender and the average seniority of the review panel for Cycles 19 and 20, but not Cycle 21. We discuss these results and some consequent changes to the proposal format and additions to the HST TAC orientation process.
    Publications of the Astronomical Society of the Pacific 09/2014; 126(944). DOI:10.1086/678964 · 3.23 Impact Factor
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    ABSTRACT: We used HST/WFC3 observations of a sample of 26 nearby ($\le$20 pc) mid to late T dwarfs to search for cooler companions and measure the multiplicity statistics of brown dwarfs. Tightly-separated companions were searched for using a double-PSF fitting algorithm. We also compared our detection limits based on simulations to other prior T5+ brown dwarf binary programs. No new wide or tight companions were identified, which is consistent with the number of known T5+ binary systems and the resolution limits of WFC3. We use our results to add new constraints to the binary fraction of T-type brown dwarfs. Modeling selection effects and adopting previously derived separation and mass ratio distributions, we find an upper limit total binary fraction of <16% and <25% assuming power law and flat mass ratio distributions respectively, which are consistent with previous results. We also characterize a handful of targets around the L/T transition.
    The Astronomical Journal 08/2014; 148(6). DOI:10.1088/0004-6256/148/6/129 · 4.05 Impact Factor
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    ABSTRACT: By reprocessing the NICMOS coronagraphic archive using improved PSF subtraction methods, we have obtained new images of 5 debris disks, all previously unseen using classical PSF subtractions. Three of the disks are edge on and two appear to be ring like, one of which is extremely asymmetric. Their stellar hosts are nearby, young F and G type stars (40-90 pc, 12-30 Myr), including one that is a close analog to the young sun at roughly the age at which terrestrial planets were assembling. This is a 25% increase in the sample of debris disks seen in scattered light. Analysis and modeling of the disk geometries is in process. Given these systems' youth, proximity, and brightness (V = 7.2 to 8.5), these will be superb targets for investigating planet formation, and are perfect targets for studies with GPI, SPHERE and JWST.
    Proceedings of the International Astronomical Union 06/2014; DOI:10.1017/S1743921313008922
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    ABSTRACT: Using Director's Discretionary observing time, HST is undertaking a revolutionary deep field observing program to peer deeper into the Universe than ever before. The Frontier Fields will combine the power of HST with the natural gravitational telescopes of high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies and the second-deepest observations of blank fields ever obtained. Up to six strong-lensing clusters (Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, AbellS1063, and Abell 370) will be targeted with coordinated parallels of adjacent blank fields with ACS/WFC and WFC3/IR cameras to ~29th ABmag depths in seven bandpasses over the next three years. These observations will reveal distant galaxy populations ~10-100 times fainter than any previously observed, and improve our statistical understanding of galaxies during the epoch of reionization. Here we present Hubble Space Telescope observations of the first set of the Frontier Fields, Abell 2744, and describe the HST Frontier Fields observing strategy and schedule. All data for this observing program is nonproprietary and available immediately upon entry into the Mikulski Archive for Space Telescopes.
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    ABSTRACT: We have spatially resolved the debris disk around the young 30 Myr) G dwarf HD 202917 through the analysis of archival HST/NICMOS coronagraphic images. The disk was revealed by reprocessing the images (HST/AR program 11279; PI Schneider) through a novel pipeline that improves the subtraction of the coronagraphic PSF (HST/AR program 12652; PI Soummer). The NICMOS scattered light image confirms an earlier, formally unpublished detection of the disk at optical wavelengths from HST/ACS coronagraph images. Together, the images show a highly inclined disk extending ~200 AU from the star. We describe preliminary disk models obtained from available photometry and resolved images of the system and the 3D radiative transfer code MCFOST (Pinte et al. 2008), which enables the reconstruction of SEDs and images according to specified dust composition and disk morphology.
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    ABSTRACT: We present a new measurement of the stellar Initial Mass Function (IMF) based on ultra-deep, high-resolution photometry of >5,000 stars in the outskirts of the Small Magellanic Cloud (SMC) galaxy. The stellar main sequence of the SMC is measured in the color-magnitude diagram (CMD) down to ~30th magnitude, and is cleanly separated from the foreground star cluster population using proper motions. We simulate the SMC population by extracting stellar masses (single and unresolved binaries) from specific IMFs, and converting those masses to luminosities in our bandpasses. The corresponding photometry for these simulated stars is drawn directly from a rich cloud of million artificial stars, thereby accounting for the real photometric scatter and completeness of the data. Over a continuous and well populated mass range of M = 0.37-0.93 Msun, we demonstrate that the IMF is well represented by a single power-law form with slope α = -1.90 ([+0.15] [-0.10]) (3 σ error) (i.e., dN/dM propto M^(α), Salpeter α = -2.35). Our results indicate that the IMF does not turn over to a more shallow power law form within this mass range.
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    ABSTRACT: The Archival Legacy Investigation of Circumstellar Environments (ALICE) project (HST/AR program 12652; PI Soummer) is currently conducting a comprehensive and consistent reprocessing of HST-NICMOS coronagraphic survey data to search for point sources and disks using advanced PSF subtraction. The Karhunen-Loeve Image Projection (KLIP) algorithm based on principal component analysis was developed for this project. We present the main concept for the pipeline, reduction strategy, and PSF subtraction implementation and performance. The ALICE pipeline was designed to process automatically approximately 400 targets in the NICMOS coronagraphic archive, and to deliver High-Level Science Products (HLSPs) back to the MAST archive at STScI. The HLSPs are defined in collaboration with other similar projects to define a standard format for high-contrast imaging. We present and discuss the ALICE point source candidates detected in the NICMOS archive together with a statistical analysis of the population of background objects.
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    ABSTRACT: We have spatially resolved four new debris disks in scattered light for the first time through the analysis of archival HST NICMOS coronagraphic images. These disks around 12-30-Myr-old main-sequence F or G stars were revealed by reprocessing recalibrated archival images (HST AR program LAPLACE; PI Schneider) with a novel pipeline that improves the subtraction of the PSF (ALICE; Soummer et al. 2012). Three of these disks (HD 30447, HD 35841, and HD 141943) appear to be edge-on, and the fourth (HD 191089) appears to be an asymmetric inclined ring. We describe our modeling efforts so far that take into account all available photometry and resolved images for these sources. We employ the 3D radiative transfer code MCFOST (Pinte et al. 2008), which enables the reconstruction of SEDs and images according to the specified dust composition and disk morphology.
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    ABSTRACT: Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used HST/WFC3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 $\mu$m for $\approx$40 min per object. Using Bayesian analysis, we find 6 brown dwarfs with confident $(p>95\%)$ variability in the relative flux in at least one wavelength region at sub-percent precision, and 5 brown dwarfs with tentative $(p>68\%)$ variability. We derive a minimum variability fraction $f_{min}=27^{+11}_{-7}\%$ over all covered spectral types. The fraction of variables is equal within errors for mid L, late L and mid T spectral types; for early T dwarfs we do not find any confident variable but the sample is too small to derive meaningful limits. For some objects, the variability occurs primarily in the flux peak in the J or H band, others are variable throughout the spectrum or only in specific absorption regions. Four sources may have broad-band peak-to-peak amplitudes exceeding 1%. Our measurements are not sensitive to very long periods, inclinations near pole-on and rotationally symmetric heterogeneity. The detection statistics are consistent with most brown dwarf photospheres being patchy. While multiple-percent near-infrared variability may be rare and confined to the L/T transition, low-level heterogeneities are a frequent characteristic of brown dwarf atmospheres.
    The Astrophysical Journal 12/2013; 782(2). DOI:10.1088/0004-637X/782/2/77 · 6.28 Impact Factor
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    ABSTRACT: In this study we compare the photometric data of 34 Milky Way globular clusters, observed within the ACS Treasury Program (PI: Ata Sarajedini) with the corresponding ground-based data, provided by the Photometric Standard Field Catalogs of Stetson (2000, 2005). We focus on the transformation between the HST/ACS F606W to V-band and F814W to I-band only. The goal is to assess the validity of the filter transformation equations by Sirianni et al.(2005) with respect to their dependence on metallicity, Horizontal Branch morphology, mass and integrated (V-I) colour of the various globular clusters. Such a dependence is expected due to the fact that the transformation equations are based on the observations of only one globular cluster, i.e., NGC 2419. Surprisingly, the correlation between offset and metallicity is found to be weak, with a low level significance. The correlation between offset and Horizontal Branch structure, as well as total cluster mass is still weaker. Based on the available data we do not find the photometric offset to be linked to multiple stellar populations, e.g., as found in NGC 0288, NGC 1851, and NGC 5139. The results of this study show that there are small systematic offsets between the transformed ACS- and observed ground based photometry, and that these are only weakly correlated, if at all, with various cluster parameters and their underlying stellar populations. As a result, investigators wishing to transform globular cluster photometry from the Sirianni et al.(2005) ground-based V, I system onto the Stetson (2000) system simply need to add 0.040 (+/-0.012) to the V-band magnitudes and 0.047 (+/-0.011) to the I-band magnitudes. This in turn means that the transformed ACS (V-I) colours match the ground-based values from Stetson (2000) to within ~0.01 mag.
    The Astrophysical Journal Supplement Series 12/2013; 211(1). DOI:10.1088/0067-0049/211/1/1 · 14.14 Impact Factor
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    ABSTRACT: We report results of a direct imaging survey for giant planets around 80 members of the Beta Pic, TW Hya, Tucana-Horologium, AB Dor, and Hercules-Lyra moving groups, observed as part of the Gemini NICI Planet-Finding Campaign. For this sample, we obtained median contrasts of \Delta H=13.9 mag at 1" in combined CH4 narrowband ADI+SDI mode and median contrasts of \Delta H=15.1 mag at 2" in H-band ADI mode. We found numerous (>70) candidate companions in our survey images. Some of these candidates were rejected as common-proper motion companions using archival data; we reobserved with NICI all other candidates that lay within 400 AU of the star and were not in dense stellar fields. The vast majority of candidate companions were confirmed as background objects from archival observations and/or dedicated NICI campaign followup. Four co-moving companions of brown dwarf or stellar mass were discovered in this moving group sample: PZ Tel B (36+-6 MJup, 16.4+-1.0 AU, Biller et al. 2010), CD -35 2722B (31+-8 MJup, 67+-4 AU, Wahhaj et al. 2011), HD 12894B (0.46+-0.08 MSun, 15.7+-1.0 AU), and BD+07 1919C (0.20+-0.03 MSun, 12.5+-1.4 AU). From a Bayesian analysis of the achieved H band ADI and ASDI contrasts, using power-law models of planet distributions and hot-start evolutionary models, we restrict the frequency of 1--20 MJup companions at semi-major axes from 10--150 AU to <18% at a 95.4% confidence level using DUSTY models and to <6% at a 95.4% using COND models.
    The Astrophysical Journal 09/2013; 777(2). DOI:10.1088/0004-637X/777/2/160 · 6.28 Impact Factor
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    ABSTRACT: We have completed a high-contrast direct imaging survey for giant planets around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign. We achieved median H-band contrasts of 12.4 mag at 0.5" and 14.1 mag at 1" separation. Follow-up observations of the 66 candidates with projected separation < 500 AU show that all of them are background objects. To establish statistical constraints on the underlying giant planet population based on our imaging data, we have developed a new Bayesian formalism that incorporates (1) non-detections, (2) single-epoch candidates, (3) astrometric and (4) photometric information, and (5) the possibility of multiple planets per star to constrain the planet population. Our formalism allows us to include in our analysis the previously known Beta Pictoris and the HR 8799 planets. Our results show at 95% confidence that <13% of debris disk stars have a >5MJup planet beyond 80 AU, and <21% of debris disk stars have a >3MJup planet outside of 40 AU, based on hot-start evolutionary models. We model the population of directly-imaged planets as d^2N/dMda ~ m^alpha a^beta, where m is planet mass and a is orbital semi-major axis (with a maximum value of amax). We find that beta < -0.8 and/or alpha > 1.7. Likewise, we find that beta < -0.8 and/or amax < 200 AU. If we ignore the Beta Pic and HR 8799 planets (should they belong to a rare and distinct group), we find that < 20% of debris disk stars have a > 3MJup planet beyond 10 AU, and beta < -0.8 and/or alpha < -1.5. Our Bayesian constraints are not strong enough to reveal any dependence of the planet frequency on stellar host mass. Studies of transition disks have suggested that about 20% of stars are undergoing planet formation; our non-detections at large separations show that planets with orbital separation > 40 AU and planet masses > 3 MJup do not carve the central holes in these disks.
    The Astrophysical Journal 08/2013; 773(2):179. DOI:10.1088/0004-637X/773/2/179 · 6.28 Impact Factor
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    ABSTRACT: The full fields covered by the HST ACS/WFC and WFPC2 surveys are shown, respectively, in Figures 2 and 3. Both are approximately centered at RA=05:35:00 and DEC=-5:26:00 (J2000), approximately 200" to the SW of the Trapezium asterism and extend over about one-sixth of a square degree. In particular, the full ACS mosaic covers 627arcmin2, whereas the WFPC2 mosaic covers 570.5arcmin2. With NICMOS, our survey covered only a fraction of the ACS field due to the limited field of view of the instrument (Figure 4). A total of 102 regions were covered in both the filter F110W and F160W bands, corresponding to about 177arcmin2 and 171.5arcmin2 in the F110W and F160W filters, respectively. In order to exchange the relative position of ACS and WFPC2, we rotated by 180° the roll angle of the HST by scheduling the observations in two epochs separated by approximately 6 months. The first epoch, executed in the fall of 2004 (2004 October 11-November 7), covered strips 2, 5, and 6 with a position angle of 280°, for a total of 36 orbits. The second epoch, executed in the spring of 2005 (2005 March 3-April 26) covered strips 0, 1, 3, 4, 7, and 8 with a position angle of 100°, for a total of 68 orbits. Both epochs and position angles were optimized to schedule the observations at the peaks of the visibility periods of the Orion Nebula. Table 2 summarizes the scheduling of our observations. Figure 6 presents the overall coverage of the survey. See section 2 for further explanations about the observations. (4 data files).
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    ABSTRACT: We have carried out high contrast imaging of 70 young, nearby B and A stars to search for brown dwarf and planetary companions as part of the Gemini NICI Planet-Finding Campaign. Our survey represents the largest, deepest survey for planets around high-mass stars (~1.5-2.5 M_sun) conducted to date and includes the planet hosts beta Pic and Fomalhaut. We obtained follow-up astrometry of all candidate companions within 400 AU projected separation for stars in uncrowded fields and identified new low-mass companions to HD 1160 and HIP 79797. We have found that the previously known young brown dwarf companion to HIP 79797 is itself a tight (3 AU) binary, composed of brown dwarfs with masses 58 (+21, -20) M_Jup and 55 (+20, -19) M_Jup, making this system one of the rare substellar binaries in orbit around a star. Considering the contrast limits of our NICI data and the fact that we did not detect any planets, we use high-fidelity Monte Carlo simulations to show that fewer than 20% of 2 M_sun stars can have giant planets greater than 4 M_Jup between 59 and 460 AU at 95% confidence, and fewer than 10% of these stars can have a planet more massive than 10 M_Jup between 38 and 650 AU. Overall, we find that large-separation giant planets are not common around B and A stars: fewer than 10% of B and A stars can have an analog to the HR 8799 b (7 M_Jup, 68 AU) planet at 95% confidence. We also describe a new Bayesian technique for determining the ages of field B and A stars from photometry and theoretical isochrones. Our method produces more plausible ages for high-mass stars than previous age-dating techniques, which tend to underestimate stellar ages and their uncertainties.
    The Astrophysical Journal 06/2013; 776(1). DOI:10.1088/0004-637X/776/1/4 · 6.28 Impact Factor
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    ABSTRACT: Most directly imaged giant exoplanets are fainter than brown dwarfs with similar spectra. To explain their relative underluminosity, unusually cloudy atmospheres have been proposed. However, with multiple parameters varying between any two objects, it remained difficult to observationally test this idea. We present a new method, sensitive time-resolved Hubble Space Telescope near-infrared spectroscopy, to study two rotating L/T transition brown dwarfs (2M2139 and SIMP0136). The observations provide spatially and spectrally resolved mapping of the cloud decks of the brown dwarfs. The data allow the study of cloud structure variations while other parameters are unchanged. We find that both brown dwarfs display variations of identical nature: J- and H-band brightness variations with minimal color and spectral changes. Our light curve models show that even the simplest surface brightness distributions require at least three elliptical spots. We show that for each source the spectral changes can be reproduced with a linear combination of only two different spectra, i.e., the entire surface is covered by two distinct types of regions. Modeling the color changes and spectral variations together reveal patchy cloud covers consisting of a spatially heterogeneous mix of low-brightness, low-temperature thick clouds and brighter, thin, and warm clouds. We show that the same thick cloud patches seen in our varying brown dwarf targets, if extended to the entire photosphere, predict near-infrared colors/magnitudes matching the range occupied by the directly imaged exoplanets that are cooler and less luminous than brown dwarfs with similar spectral types. This supports the models in which thick clouds are responsible for the near-infrared properties of these "underluminous" exoplanets.
    The Astrophysical Journal 04/2013; 768(2):121. DOI:10.1088/0004-637X/768/2/121 · 6.28 Impact Factor
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    ABSTRACT: The Hubble Space Telescope (HST) Treasury Program on the Orion Nebula Cluster has used 104 orbits of HST time to image the Great Orion Nebula region with the Advanced Camera for Surveys (ACS), the Wide-Field/Planetary Camera 2 (WFPC2) and the Near Infrared Camera and Multi Object Spectrograph (NICMOS) instruments in 11 filters ranging from the U-band to the H-band equivalent of HST. The program has been intended to perform the definitive study of the stellar component of the ONC at visible wavelengths, addressing key questions like the cluster IMF, age spread, mass accretion, binarity and cirumstellar disk evolution. The scanning pattern allowed to cover a contiguous field of approximately 600 square arcminutes with both ACS and WFPC2, with a typical exposure time of approximately 11 minutes per ACS filter, corresponding to a point source depth AB(F435W) = 25.8 and AB(F775W)=25.2 with 0.2 magnitudes of photometric error. We describe the observations, data reduction and data products, including images, source catalogs and tools for quick look preview. In particular, we provide ACS photometry for 3399 stars, most of them detected at multiple epochs, WFPC2 photometry for 1643 stars, 1021 of them detected in the U-band, and NICMOS JH photometry for 2116 stars. We summarize the early science results that have been presented in a number of papers. The final set of images and the photometric catalogs are publicly available through the archive as High Level Science Products at the STScI Multimission Archive hosted by the Space Telescope Science Institute.
    The Astrophysical Journal Supplement Series 04/2013; 207(1). DOI:10.1088/0067-0049/207/1/10 · 14.14 Impact Factor
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    ABSTRACT: The physics and chemistry of condensate clouds play pivotal but poorly understood roles in the atmospheric structure and composition of ultracool brown dwarfs and giant exoplanets. Unresolved observations can only provide limited insights into the structure of clouds or the processes behind the transition from the cloudy L-type sources to the cloud-free T-type ones. We will review exciting results from a new technique, rotational phase mapping, of ultracool atmospheres. Using precision infrared Spitzer photometry and HST spectroscopy covering entire rotation periods of brown dwarfs, we have obtained detailed spectrally and spatially resolved information of their atmospheres. The key results include the identification of cloud structures in L/T brown dwarfs, evidence for longitudinal and vertical cloud heterogeneities, and spectral constraints on the composition and types of clouds. We show that L/T transition brown dwarfs often have thin cloud covers with patches of cold, thick clouds, which introduce strong but only weakly wavelength-dependent extinction. The same thick cloud patches seen in our varying brown dwarf targets, if extended to the entire surface, predict near-infrared colors/magnitudes matching the range occupied by the "underluminous" directly imaged exoplanets. This supports the models in which thick clouds are responsible for the near-infrared properties of underluminous exoplanets.
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    ABSTRACT: We present a new measurement of the stellar initial mass function (IMF) based on ultra-deep, high-resolution photometry of >5,000 stars in the outskirts of the Small Magellanic Cloud (SMC) galaxy. The Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) observations reveal this rich, co-spatial population behind the foreground globular cluster 47 Tuc, which we targeted for 121 HST orbits. The stellar main sequence of the SMC is measured in the F606W, F814W color-magnitude diagram (CMD) down to ~30th magnitude, and is cleanly separated from the foreground star cluster population using proper motions. We simulate the SMC population by extracting stellar masses (single and unresolved binaries) from specific IMFs, and converting those masses to luminosities in our bandpasses. The corresponding photometry for these simulated stars is drawn directly from a rich cloud of 4 million artificial stars, thereby accounting for the real photometric scatter and completeness of the data. Over a continuous and well populated mass range of M = 0.37 - 0.93 Msun (i.e., down to a ~75% completeness limit at F606W = 28.7), we demonstrate that the IMF is well represented by a single power-law form with slope \alpha = -1.90 (^{+0.15}_{-0.10}) (3 sigma error) (i.e., dN/dM \propto M^{\alpha}). This is shallower than the Salpeter slope of \alpha = -2.35, which agrees with the observed stellar luminosity function at higher masses. Our results indicate that the IMF does {\it not} turn over to a more shallow power-law form within this mass range. We discuss implications of this result for the theory of star formation, the inferred masses of galaxies, and the (lack of a) variation of the IMF with metallicity.
    The Astrophysical Journal 12/2012; 763(2). DOI:10.1088/0004-637X/763/2/110 · 6.28 Impact Factor
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    ABSTRACT: Heterogeneous clouds or temperature perturbations in rotating brown dwarfs produce variability in the observed flux. We report time-resolved simultaneous observations of the variable T6.5 brown dwarf 2MASSJ22282889-431026 over the wavelength ranges 1.1-1.7 microns and broadband 4.5 microns. Spectroscopic observations were taken with Wide Field Camera 3 on board the Hubble Space Telescope and photometry with the Spitzer Space Telescope. The object shows sinusoidal infrared variability with a period of 1.4 hr at most wavelengths with peak-to-peak amplitudes between 1.45% and 5.3% of the mean flux. While the light curve shapes are similar at all wavelengths, their phases differ from wavelength to wavelength with a maximum difference of more than half of a rotational period. We compare the spectra with atmospheric models of different cloud prescriptions, from which we determine the pressure levels probed at different wavelengths. We find that the phase lag increases with decreasing pressure level, or higher altitude. We discuss a number of plausible scenarios that could cause this trend of light curve phase with probed pressure level. These observations are the first to probe heterogeneity in an ultracool atmosphere in both horizontal and vertical directions, and thus are an ideal test case for realistic three dimensional simulations of the atmospheric structure with clouds in brown dwarfs and extrasolar planets.
    The Astrophysical Journal Letters 10/2012; 760(2). DOI:10.1088/2041-8205/760/2/L31 · 5.60 Impact Factor

Publication Stats

8k Citations
814.27 Total Impact Points

Institutions

  • 2001–2014
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 2013
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 1997–2009
    • California Institute of Technology
      • Infrared Processing and Analysis Center
      Pasadena, California, United States
  • 2008
    • University of Exeter
      Exeter, England, United Kingdom
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 1999–2008
    • University of Pennsylvania
      • Department of Physics and Astronomy
      Philadelphia, PA, United States
  • 2007
    • American Museum of Natural History
      • Division of Physical Sciences
      New York City, New York, United States
  • 1999–2001
    • University of Virginia
      • Department of Astronomy
      Charlottesville, Virginia, United States
  • 1998
    • University of Massachusetts Amherst
      • Department of Astronomy
      Amherst Center, Massachusetts, United States