Search

Space-based stellar coronagraph instruments aim to directly image exoplanets that are a fraction of an arcsecond separation and ten billion times fainter than their host star. To achieve this, one or more deformable mirrors (DMs) are used in concert with coronagraph masks to control the wavefront and minimize diffracted starlight in a region of the image known as the ``dark zone" or ``dark hole." The DMs must have a high number of actuators (50 to 96 across) to allow dark holes that are large enough to image a range of desired exoplanet separations. In addition, the surfaces of the DMs must be controlled at the picometer level to enable the required contrast. Any defect in the mechanical structure of the DMs or electronic system could significantly impact the scientific potential of the mission. Thus, NASA's Exoplanet Exploration Program (ExEP) procured two 50$\times$50 microelectromechanical (MEMS) DMs manufactured by Boston Micromachines Corporation (BMC) to test their robustness to the vibrational environment that the DMs will be exposed to during launch. The DMs were subjected to a battery of functional and high-contrast imaging tests before and after exposure to flight-like random vibrations. The DMs did not show any significant functional nor performance degradation at $10^{-8}$ contrast levels., Comment: Accepted for publication in JATIS

The Astro2020 report outlines numerous recommendations that could significantly advance technosignature science. Technosignatures refer to any observable manifestations of extraterrestrial technology, and the search for technosignatures is part of the continuum of the astrobiological search for biosignatures. The search for technosignatures is directly relevant to the "World and Suns in Context" theme and "Pathways to Habitable Worlds" program in the Astro2020 report. The relevance of technosignatures was explicitly mentioned in "E1 Report of the Panel on Exoplanets, Astrobiology, and the Solar System," which stated that "life's global impacts on a planet's atmosphere, surface, and temporal behavior may therefore manifest as potentially detectable exoplanet biosignatures, or technosignatures" and that potential technosignatures, much like biosignatures, must be carefully analyzed to mitigate false positives. The connection of technosignatures to this high-level theme and program can be emphasized, as the report makes clear the purpose is to address the question "Are we alone?" This question is also presented in the Explore Science 2020-2024 plan as a driver of NASA's mission. This white paper summarizes the potential technosignature opportunities within the recommendations of the Astro2020 report, should they be implemented by funding agencies. The objective of this paper is to demonstrate the relevance of technosignature science to a wide range of missions and urge the scientific community to include the search for technosignatures as part of the stated science justifications for the large and medium programs that include the Infrared/Optical/Ultraviolet space telescope, Extremely Large Telescopes, probe-class far-infrared and X-ray missions, and various facilities in radio astronomy., Comment: Unsolicited white paper by the NExSS Working Group on Technosignatures, 11 pages

In support of the National Acadamies' Exoplanet Science Strategy, this whitepaper outlines key technology challenges for studying the diversity of worlds in the Galaxy and in searching for habitable planets. Observations of habitable planets outside of our solar system require technologies enabling the measurement of (1) spectral signatures of gases in their atmospheres, some of which may be of biological origin, and (2) planetary mass. Technology gaps must be closed in many areas. In some cases, performance requirements are 1-2 orders of magnitude from the current state-of-the-art. Thes technology gaps are in the areas of: starlight suppression (for reflection or emission spectroscopy; coronagraphs or starshades, contrast stability, detector sensitivity, collecting area, spectroscopic sensitivity, radial stellar motion sensitivity, and tangential stellar motion sensitivity. The technologies advancing to close these gaps are identified through the NASA Exoplanet Exploration Program's (ExEP's) annual Technology Selection and Prioritization Process in collaboration with the larger exoplanet science and technology communities. Details can be found in the annual ExEP Technology Plan Appendix. Looking towards the more distant future, the size of a desired single-aperture space telescope, even when folded, may exceed current launch capabilities, suggesting the study of in-space assembly approaches. Additionally, mid-infrared spectral observations of candidate habitable worlds may be needed to rule out false positives observed at shorter wavelengths and add supportive evidence. Consequently, single aperture telescopes may prove impractically large and space interferometry may be needed, as identified in NASA's 30 year roadmap Enduring Quests, Daring Visions, Comment: arXiv admin note: substantial text overlap with arXiv:1801.07811

For the first time in human history, we will soon be able to apply the scientific method to the question "Are We Alone?" The rapid advance of exoplanet discovery, planetary systems science, and telescope technology will soon allow scientists to search for life beyond our Solar System through direct observation of extrasolar planets. This endeavor will occur alongside searches for habitable environments and signs of life within our Solar System. While the searches are thematically related and will inform each other, they will require separate observational techniques. The search for life on exoplanets holds potential through the great diversity of worlds to be explored beyond our Solar System. However, there are also unique challenges related to the relatively limited data this search will obtain on any individual world. This white paper reviews the scientific community's ability to use data from future telescopes to search for life on exoplanets. This material summarizes products from the Exoplanet Biosignatures Workshop Without Walls (EBWWW). The EBWWW was constituted by a series of online and in person activities, with participation from the international exoplanet and astrobiology communities, to assess state of the science and future research needs for the remote detection of life on planets outside our Solar System., Comment: This is a white paper that was submitted to the National Academies of Sciences Study: Astrobiology Science Strategy for the Search for Life in the Universe

We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (~ 6 - 10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24 microns. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii ~ 0.1 to ~ 10AU from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ~ 1 to ~ 18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 micron excesses ([8] - [24] > 1.5) increases from 8.4 +\- 1.3% at ~ 3 Myr to 46 +\- 5% at ~ 10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend., Comment: accepted by the Astrophysical Journal

We present the discovery of 2MASS J21321145+1341584AB as a closely separated (0.066") very low-mass field dwarf binary resolved in the near-infrared by the Keck II Telescope using laser guide star adaptive optics. Physical association is deduced from the angular proximity of the components and constraints on their common proper motion. We have obtained a near-infrared spectrum of the binary and find that it is best described by an L5+/-0.5 primary and an L7.5+/-0.5 secondary. Model-dependent masses predict that the two components straddle the hydrogen burning limit threshold with the primary likely stellar and the secondary likely substellar. The properties of this sytem - close projected separation (1.8+/-0.3 AU) and near unity mass ratio - are consistent with previous results for very low-mass field binaries. The relatively short estimated orbital period of this system (~7-12 yr) makes it a good target for dynamical mass measurements. Interestingly, the system's angular separation is the tightest yet for any very low-mass binary published from a ground-based telescope and is the tightest binary discovered with laser guide star adaptive optics to date., Comment: 10 pages, 3 figures; accepted for publication to AJ

Direct imaging of an Earth-like exoplanet will require future missions, such as the proposed HabEx or LUVOIR concepts, to achieve starlight suppression with planet/star contrast ratios on the order of 10−10 at angular separations <100 milliarcseconds in visible wavelengths. To facilitate the technology and algorithm development required to enable this ambitious scientific goal, NASA’s Exoplanet Exploration Program (ExEP) High Contrast Imaging Testbed (HCIT) facility at the Jet Propulsion Laboratory (JPL) recently commissioned the Decadal Survey Testbed (DST), a state-of-the-art, flexible, and extremely stable coronagraph testbed. This testbed integrates years of experience and lessons learned at HCIT and has now demonstrated contrast ratios as low as few times 10−10 in 10% bandwidth. Following the success of DST, the HCIT team has developed a companion testbed, the Decadal Survey Testbed 2 (DST2) that further implements lessons learned from DST, and will provide the HCIT with additional coronagraph testbed capacity and efficiency. Commissioning for DST2 is currently targeted for Fall 2021. Here we provide an update on the status of DST, and report on the design, performance modeling simulations, and status of integration and testing for DST2, highlighting updates to the design from the original DST.

We report laboratory results of a coronagraphic test bench to assess the intensity reduction differences between a "Gaussian" tapered focal plane coronagraphic mask and a classical hard-edged "Top Hat" function mask at Extreme Adaptive Optics (ExAO) Strehl ratios of ~94%. However, unlike a traditional coronagraph design, we insert a reflective focal plane mask at 45 degree to the optical axis. We also used an intermediate secondary mask ("Mask_2") before a final image in order to block additional mask-edge diffracted light. The test bench simulates the 8.1m Gemini North telescope. It includes one spider vane, different mask radii (r= 1.9, 3.7, 7.4 lambda/D) and two types of reflective focal plane masks (hard-edged "Top Hat" and "Gaussian" tapered profiles). In order to investigate the relative performance of these competing coronagraphic designs with regard to extra-solar planet detection sensitivity, we utilize the simulation of realistic extra-solar planet populations (Nielson et al. 2006). With an appropriate translation of our laboratory results to expected telescope performance, a "Gaussian" tapered mask radius of 3.7 lambda/D with an additional mask ("Mask_2") performs best (highest planet detection sensitivity). For a full survey with this optimal design, the simulation predicts ~30% more planets detected compared to a similar sized "Top Hat" function mask with "Mask_2." Using the best design, the point contrast ratio between the stellar PSF peak and the coronagraphic PSF at 10 lambda/D (0.4" in H band if D = 8.1m) is ~10 times higher than a classical Lyot "Top Hat" coronagraph. Hence, we find a Gaussian apodized mask with an additional blocking mask is a superior (~10x higher contrast) than use of a classical Lyot coronagraph for ExAO-like Strehls., Comment: 42 pages, 12 figures, 1 table: accepted by the Publications of the Astronomical Society of the Pacific

We present results of a high-resolution, near-infrared survey of 41 nearby, young (<~300 Myr) M0-M5.0 dwarfs using the Altair natural guide star adaptive optics system at the Gemini North telescope. Twelve of the objects appear to be binaries, 7 of which are reported here for the first time. One triple system was discovered. Statistical properties are studied and compared with earlier (F to K) and later (>= M6 very low-mass, VLM) populations. We find that the separation distribution of the binaries in this sample peaks at 13+14-9 AU, which is consistent with previous measurements of early-M binaries. Hence, early-M binaries seem to occur in--on average--tighter systems than G binaries. At the same time they are significantly wider than field VLM binary stars. The distribution of mass ratios q of primary and secondary stars was found to show an intermediate distribution between the strongly q-->1 peaked distribution of field VLM systems and the almost flat distribution of earlier-type stars. Consequently, we show evidence for relatively young, early-M binaries representing a transition between the well known earlier star distributions and the recently examined field VLM population characteristics. Despite the fact that this survey was dedicated to the search for faint brown dwarf and planetary mass companions, all planetary mass candidates were background objects. We exclude the existence of physical companions with masses greater than 10 Jupiter masses (M_Jup) at separations of >~40 AU and masses greater than 24 M_Jup for separations >~10 AU around 37 of the 41 observed objects., Comment: To appear in the January 1, 2007 issue of the Astrophysical Journal, 12 pages, 13 figures. Minor typographical and grammatical changes. Wrong round off in binary fraction corrected

We present 24 micron Spitzer/MIPS photometric observations of the ~50 Myr open cluster IC 2391. Thirty-four cluster members ranging in spectral type from B3-M5 were observed in the central square degree of the cluster. Excesses indicative of debris disks were discovered around 1 A star, 6 FGK stars, and possibly 1 M dwarf. For the cluster members observed to their photospheric limit, we find a debris disk frequency of 10 (-3,+17)% for B-A stars and 31 (-9,+13)% for FGK stars using a 15% relative excess threshold. Relative to a model of decaying excess frequency, the frequency of debris disks around A-type stars appears marginally low for the cluster's age while that of FGK stars appears consistent. Scenarios that may qualitatively explain this result are examined. We conclude that planetesimal activity in the terrestrial region of FGK stars is common in the first ~50 Myr and decays on timescales of ~100 Myr. Despite luminosity differences, debris disk evolution does not appear to depend strongly on stellar mass., Comment: total 23 pages including 7 figures, accepted for publication in ApJ

We imaged five objects near the star forming clouds of Ophiuchus with the Keck Laser Guide Star AO system. We resolved Allers et al. (2006)'s #11 (Oph 16222-2405) and #16 (Oph 16233-2402) into binary systems. The #11 object is resolved into a 243 AU binary, the widest known for a very low mass (VLM) binary. The binary nature of #11 was discovered first by Allers (2005) and independently here during which we obtained the first spatially resolved R~2000 near-infrared (J & K) spectra, mid-IR photometry, and orbital motion estimates. We estimate for 11A and 11B gravities (log(g)>3.75), ages (5+/-2 Myr), luminosities (log(L/Lsun)=-2.77+/-0.10 and -2.96+/-0.10), and temperatures (Teff=2375+/-175 and 2175+/-175 K). We find self-consistent DUSTY evolutionary model (Chabrier et al. 2000) masses of 17+4-5 MJup and 14+6-5 MJup, for 11A and 11B respectively. Our masses are higher than those previously reported (13-15 MJup and 7-8 MJup) by Jayawardhana & Ivanov (2006b). Hence, we find the system is unlikely a ``planetary mass binary'', (in agreement with Luhman et al. 2007) but it has the second lowest mass and lowest binding energy of any known binary. Oph #11 and Oph #16 belong to a newly recognized population of wide (>100 AU), young (<10 Myr), roughly equal mass, VLM stellar and brown dwarf binaries. We deduce that ~6+/-3% of young (<10 Myr) VLM objects are in such wide systems. However, only 0.3+/-0.1% of old field VLM objects are found in such wide systems. Thus, young, wide, VLM binary populations may be evaporating, due to stellar encounters in their natal clusters, leading to a field population depleted in wide VLM systems., Comment: Accepted version V2. Now 13 pages longer (45 total) due to a new discussion of the stability of the wide brown dwarf binary population, new summary Figure 17 now included, Astrophysical Journal 2007 in press

We performed a 24 micron 2 Deg X 1 Deg survey of the Pleiades cluster, using the MIPS instrument on Spitzer. Fifty four members ranging in spectral type from B8 to K6 show 24 micron fluxes consistent with bare photospheres. All Be stars show excesses attributed to free-free emission in their gaseous envelopes. Five early-type stars and four solar-type stars show excesses indicative of debris disks. We find a debris disk fraction of 25 % for B-A members and 10 % for F-K3 ones. These fractions appear intermediate between those for younger clusters and for the older field stars. They indicate a decay with age of the frequency of the dust-production events inside the planetary zone, with similar time scales for solar-mass stars as have been found previously for A-stars., Comment: accepted to ApJ

We present observations of six late-type members of the young cluster IC 348 detected at 24 microns with the Multiband Imaging Photometer for Spitzer(MIPS). At least four of the objects are probably substellar. Combining these data with ground-based optical and near-infrared photometry and complementary observations with the Infrared Array Camera (IRAC), we have modeled the spectral energy distributions using detailed models of irradiated accretion disks. We are able to fit the observations with models using a range of maximum grain sizes from ISM-type dust to grains as large as 1 millimeter. Two objects show a lack of excess emission at wavelengths shortward of 5.8-8 microns but significant excess at longer wavelengths, indicative of large optically thin or evacuated inner holes. Our models indicate a inner hole of radius ~ 0.5-0.9 AU for the brown dwarf L316; this is the first brown dwarf with evidence for an AU-scale inner disk hole. We examine several possible mechanisms for the inner disk clearing in this case, including photoevaporation and planet formation., Comment: 24 pages, 6 figures (one in PNG format). Accepted to ApJ

The properties of multiple stellar systems have long provided important empirical constraints for star formation theories, enabling (along with several other lines of evidence) a concrete, qualitative picture of the birth and early evolution of normal stars. At very low masses (VLM; M <~ 0.1 M_sun), down to and below the hydrogen burning minimum mass, our understanding of formation processes is not as clear, with several competing theories now under consideration. One means of testing these theories is through the empirical characterization of VLM multiple systems. Here, we review the results of various VLM multiplicity studies to date. These systems can be generally characterized as closely separated (93% have projected separations Delta < 20 AU) and near equal-mass (77% have M_2/M_1 >= 0.8) occurring infrequently (perhaps 10-30%). Both the frequency and maximum separation of stellar and brown dwarf binaries steadily decrease for lower system masses, suggesting that VLM binary formation and/or evolution may be a mass-dependent process. There is evidence for a fairly rapid decline in the number of loosely-bound systems below ~0.3 M_sun, corresponding to a factor of 10-20 increase in the minimum binding energy of VLM binaries as compared to more massive stellar binaries. This wide-separation ``desert'' is present among both field (~1-5 Gyr) and older (> 100 Myr) cluster systems, while the youngest (<~10 Myr) VLM binaries, particularly those in nearby, low-density star forming regions, appear to have somewhat different systemic properties. We compare these empirical trends to predictions laid out by current formation theories, and outline future observational studies needed to probe the full parameter space of the lowest mass multiple systems., Comment: 16 pages, 7 figures, contributed chapter for Planets and Protostars V meeting (October 2005); full table of VLM binaries can be obtained at http://paperclip.as.arizona.edu/~nsiegler/VLM_binaries

We present new Spitzer Space Telescope observations of the young cluster NGC2264. Observations at 24 micron with the Multiband Imaging Photometer has enabled us to identify the most highly embedded and youngest objects in NGC2264. This letter reports on one particular region of NGC2264 where bright 24 micron sources are spatially configured in curious linear structures with quasi-uniform separations. The majority of these sources (~60% are found to be protostellar in nature with Class I spectral energy distributions. Comparison of their spatial distribution with sub-millimeter data from Wolf-Chase (2003) and millimeter data from Peretto et al. (2005) shows a close correlation between the dust filaments and the linear spatial configurations of the protostars, indicating that star formation is occurring primarily within dense dusty filaments. Finally, the quasi-uniform separations of the protostars are found to be comparable in magnitude to the expected Jeans length suggesting thermal fragmentation of the dense filamentary material., Comment: Accepted for publication in ApJL, 5 pages, 4 figures. Color version available from the following webpages: http://cfa-www.harvard.edu/~pteixeir/ and http://cfa-www.harvard.edu/~clada/

We present updated results of a high-resolution, magnitude limited (Ks<12 mag) imaging survey of nearby low-mass M6.0-M7.5 field stars. The observations were carried out using adaptive optics at the Gemini North, VLT, Keck II, and Subaru telescopes. Our sample of 36 stars consists predominantly of nearby (<30 pc) field stars, 5 of which we have resolved as binaries. Two of the binary systems, 2MASSI J0429184-312356 and 2MASSI J1847034+552243, are presented here for the first time. All 5 discovered binary systems have separations between 0.08"-0.53" (2-9 AU) with similar mass ratios (q>0.8, delta Ks < 1 mag). This result supports the hypothesis that wide (a>20 AU) very low-mass (M_tot<0.19 M_sun) binary systems are rare. The projected semimajor axis distribution of these systems peak at ~ 5 AU and we report a sensitivity-corrected binary fraction of 9% (-3%, +4%) for stars with primaries of spectral type M6.0-M7.5 with separations >3 AU and mass ratios q>0.6. Within these instrumental sensitivities, these results support the overall trend that both the semimajor axis distribution and binary fraction are a function of the mass of the primary star and decrease with decreasing primary mass. These observations provide important constraints for low-mass binary star formation theories., Comment: 20 pages, 8 figures, accepted to ApJ

We present the first scientific images obtained with a deformable secondary mirror adaptive optics system. We utilized the 6.5m MMT AO system to produce high-resolution (FWHM=0.07'') near infrared (1.6 um) images of the young (~1 Myr) Orion Trapezium theta 1 Ori cluster members. A combination of high spatial resolution and high signal to noise allowed the positions of these stars to be measured to within ~0.003'' accuracies. Including previous speckle data (Weigelt et al. 1999), we analyze a six year baseline of high-resolution observations of this cluster. Over this baseline we are sensitive to relative proper motions of only ~0.002''/yr (4.2 km/s at 450 pc). At such sensitivities we detect orbital motion in the very tight theta 1 Ori B2B3 (52 AU separation) and theta 1 Ori A1A2 (94 AU separation) systems. Such motions are consistent with those independently observed by Schertl et al. (2003) with speckle interferometry, giving us confidence that these very small (~0.002''/yr) orbital motions are real. All five members of the theta 1 Ori B system appear likely gravitationally bound. The very lowest mass member of the theta 1 Ori B system (B4) has K' ~11.66 and an estimated mass of ~0.2 Msun. There was very little motion (4+/-15 km/s) detected of B4 w.r.t B1 or B2, hence B4 is possibly part of the theta 1 Ori B group. We suspect that if this very low mass member is physically associated it most likely is in an unstable (non-hierarchical) orbital position and will soon be ejected from the group. The theta 1 Ori B system appears to be a good example of a star formation ``mini-cluster'' which may eject the lowest mass members of the cluster in the near future. This ``ejection'' process could play a major role in the formation of low mass stars and brown dwarfs., Comment: To appear in the December 10, 2003 issue of the Astrophysical Journal 21 pages, 14 figures (some in color, but print OK in B&W)

A survey of 30 nearby M6.0-M7.5 dwarfs with Ks<12 mag utilizing the Hokupa'a adaptive optics system at the Gemini North Telescope has discovered 3 new binary systems. All 3 systems have separations between 0.12-0.29 arcsec (3-10 AU) with similar mass ratios (q>0.8, Delta Ks<0.7). This result gives further support to the suggestion that wide (a>20 AU) very low mass (M_{tot}<0.185 M_sun) binary systems are exceedingly rare or perhaps even non-existant. The semimajor axis distribution of these systems peaks at ~5 AU, tighter than more massive M and G binary distributions which have a broad peak at separations of \~30 AU. We find a sensitivity-corrected binary fraction in the range of 5_{-2}^{+4}% for M6.0-M7.5 stars with separations a>3 AU. This binary frequency is less than the ~32% measured among early M dwarfs over the same separation range. Two of the low-mass binaries are probable Hyades open cluster members based on proper motions, cluster membership probabilities, radial velocities, and near-IR photometry. LP415-20 has the distinction of being the tightest (3.6 AU) multiple system ever spatially resolved in the cluster and the companions of LP415-20 and LP475-855 are among the least massive objects ever resolved in the Hyades with estimated masses of 0.081_{-0.010}^{+0.009} and 0.082_{-0.009}^{+0.009} M_{\sun}., Comment: 24 pages, 9 figures, to appear in ApJ,v598, n2, December 1, 2003 issue

Use of the highly sensitive Hokupa'a/Gemini curvature wavefront sensor has allowed direct adaptive optics (AO) guiding on very low mass (VLM) stars with SpT=M8.0-L0.5. A survey of 39 such objects detected 9 VLM binaries. Most of these systems are tight (separation <5 AU) and have similar masses (Delta Ks<0.8 mag; 0.852.6 AU. This is slightly less than the 32+/-9% measured for more massive M0-M4 dwarfs over the same separation range (Fischer & Marcy 1992). It appears M8.0-L0.5 binaries (as well as L and T dwarf binaries) have a much smaller semi-major axis distribution peak (~4 AU) than early M binaries. We also find no VLM binary systems (defined here as systems with M_tot<0.185 solar masses) with separations >15 AU. We briefly explore possible reasons why VLM binaries are slightly less common, nearly equal mass, and much more tightly bound compared to more massive binaries. We find that a kick during the ejection of a forming VLM binary from a close triple or quadruple encounter (imparting a differential kick of ~3 km/s between the members of the binary) could reproduce the observed cut-off in the semi-major axis distribution at ~20 AU. However, the estimated binarity (~<5%; Bate et al. 2002) produced by such "ejection scenarios" is below the 9-15% observed. Similarly, the dynamical decay models of Sterzik & Durisen (1998); Durisen, Sterzik, & Pickett (2001) also cannot produce a VLM binary fraction above ~5%. Our estimate of a fragmentation-produced VLM binary semi-major axis distribution contains a significant fraction of ``wide'' VLM binaries with a>20 AU in contrast to observation. Hence more detailed theoretical work will be needed to explain this very interesting VLM binary population., Comment: To appear in the April 10, 2003 issue of The Astrophysical Journal 30 pages, 17 figures

Using the adaptive optics system, Hokupa'a, at Gemini-North, we have directly imaged a companion around the UKIRT faint standard M8 star, LHS 2397a (FS 129) at a separation of 2.96 AU. Near-Infrared photometry of the companion has shown it to be an L7.5 brown dwarf and confirmed the spectral type of the primary to be M8. We also derive a substellar mass of the companion of 0.068 Msun, although masses in the range (0.061-0.069) are possible, and the primary mass as 0.090 Msun (0.089-0.094). Reanalysis of archival imaging from HST has confirmed the secondary as a common proper motion object. This binary represents the first clear example of a brown dwarf companion within 4 AU of a low mass star and should be one of the first late L dwarfs to have a dynamical mass. As part of a larger survey of M8-L0 stars, this object may indicate that there is no ``brown dwarf desert'' around low mass primaries., Comment: 17 pages, 3 figures, Accepted for publication in the Astrophysical Journal

Use of the highly sensitive Hokupa'a/Gemini curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on M8-M9 very low mass (VLM) stars. An initial survey of 20 such objects (SpT=M8-M9) discovered 4 binaries. Three of the systems have separations of less than 4.2 AU and similar mass ratios (Delta K<0.8 mag; 0.853 AU. This is likely consistent with the 23+/-5% measured for more massive (M0-M6) stars over the same separation range. It appears M8-M9 binaries have a much smaller semi-major axis distribution peak (~4 AU; with no systems wider than 15 AU) compared to M and G stars which have a broad peak at larger \~30 AU separations., Comment: Accepted in Astrophysical Letters (March). 12 pages, 2 figures

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN

UNKNOWN