High-resolution Imaging Survey Research Articles

A High-resolution Imaging Survey of Massive Young Stellar Objects in the Magellanic Clouds

Constraints on the binary fraction of massive young stellar objects (mYSOs) are important for binary and massive star formation theory. Here, we present speckle imaging of 34 mYSOs located in the Large Magellanic Cloud (1/2 Z ⊙) and Small Magellanic Cloud (∼1/5 Z ⊙), probing projected separations in the 2000 to 20,000 au (at angular scales of 0.″02–0.″2) range, for stars above 8 M ⊙. We find two wide binaries in the Large Magellanic Cloud (from a sample of 23 targets), but none in a sample of 11 in the Small Magellanic Cloud, leading us to adopt a wide binary fraction of 9% ± 5% and <5%, respectively. We rule out a wide binary fraction greater than 35% in the Large Magellanic Cloud and 38% in the Small Magellanic Cloud at the 99% confidence level. This is in contrast to the wide binary fraction of mYSOs in the Milky Way (presumed to be 1 Z ⊙), which within the physical parameter space probed by this study is ∼15%–60% from the literature. We argue that while selection effects could be responsible for the lower binary fraction observed, it is more likely that there are underlying physical mechanisms responsible for the observed properties. This indicates that metallicity and environmental effects may influence the formation of wide binaries among massive stars. Future larger, more statistically significant samples of high-mass systems in low-metallicity environments for comparison to the Milky Way, are essential to confirm or repudiate our claim.

The AstraLux-TESS high spatial resolution imaging survey

Context. Chance-aligned sources or blended companions can cause false positives in planetary transit detections or simply bias the determination of the candidate properties. In the era of high-precision space-based photometers, the need for high spatial resolution images has been demonstrated to be critical for validating and confirming transit signals. This already applied to theKeplermission, is now applicable to the TESS survey, and will be critical for the PLATO mission.Aims. In this paper we present the results of the AstraLux-TESS survey, a catalog of high spatial resolution images obtained with the AstraLux instrument at the Calar Alto observatory (Almería, Spain) in the context of the TESS Follow-up Observing Program.Methods. We used the lucky imaging technique to obtain high spatial resolution images from planet candidate hosts included mostly in two relevant regimes: exoplanet candidates belonging to the level one requirement of the TESS mission (planets with radiiR &lt;4R⊕) and TESS planet candidates around intermediate-mass main-sequence stars.Results. Among the 185 planet host candidate stars observed, we found 13 (7%) to be accompanied by additional sources within a separation of 2.2 arcsec. Among them, six are not associated with sources in theGaiaDR3 catalog, thus contaminating the TESS light curve. Even if no contaminants have been detected, we can provide upper limits and probabilities to the possible existence of field contaminants through the sensitivity limits of our images. Among the isolated hosts, we can discard hazardous companions (bright enough to mimic a planetary transit signals) with an accuracy below 1% for all their planets.Conclusions. The results from this catalog are key to the statistical validation of small planets (prime targets of the TESS mission) and planets around intermediate-mass stars in the main sequence. These two populations of planets are difficult to confirm with the radial velocity technique because of the shallow amplitude of small planets and the high rotational velocities and low number of available spectral lines in the intermediate stellar mass regime. Our results also demonstrate the importance of this type of follow-up observation for future transit missions such as PLATO, even in theGaiaera.

Lithospheric structures of the eastern Himalayas as revealed by receiver function analysis

Although the Himalayan-Tibetan orogen is a result of compressional tectonics, the orogen also hosts active rifts accommodating east-west extension orthogonal to the north-south India-Asia convergence. In this study we address the question of how the north-trending rifts were formed by conducting high-resolution seismic imaging survey across southeastern Tibet where the Cona rift is exposed. Our work shows that the crustal structures of this youngest rift in southern Tibet was constructed by multiple-scale structures that are decoupled with depth and long rift trend. We suggest this deformation style to have resulted from eastward extrusion of the middle and upper crust with increasing speeds to the north towards the Yarlunbg-Zangpo suture. The differential eastward extrusion in turn may have contributed to the formation and evolution of the eastern Himalayan syntaxis.

The Study of Helium Variations in Star Clusters Using China Space Station Telescope

The China Space Station Telescope (CSST) is a 2 m space-based optical-UV telescope. Its primary goal is to carry out a high-resolution photometric imaging survey of a 17,500 square degree sky area using the on board Survey Camera. With its wide field of view (1.1 square degrees) and a mosaic imager containing 640 million pixels, studying the different populations of stars within star clusters is highly feasible. The aim of this study is to assess the CSST’s ability to distinguish between stellar populations with varying helium abundance levels, with the help of Modules for Experiments in Stellar Astrophysics. The results of the CSST’s photometry for these different populations are presented by transferring the models into the CSST Survey Camera photometric system. The findings confirm that helium-enriched stellar populations will have unique patterns in the color–magnitude diagrams under the CSST photometric system, compared to normal stellar populations. The CSST, with its filters and wide field of view of the Survey Camera, provides a new avenue for the study of multiple populations in star clusters.

UAV High-Resolution Imaging and Disease Surveys Combine to Quantify Climate-Related Decline in Seagrass Meadows

Seagrass meadows are essential habitats that support marine biodiversity and coastal communities while sequestering carbon, filtering water, and stabilizing coastal sediments. Warming temperatures stress seagrass meadows and can facilitate seagrass wasting disease, contributing to large-scale diebacks of seagrass meadows. Here, we demonstrate how high-resolution imagery, collected by uncrewed aerial vehicle (UAV) and validated by in situ sampling, can quantify seagrass responses to disease and thermal stress.

Optical and Near-infrared Excesses are Correlated in T Tauri Stars

Abstract Accretion is one of the defining characteristics of classical T Tauri stars, fueled by the presence of a circumstellar disk comprised of dust and gas. Accretion produces a UV and optical excess, while re-radiated emission at the inner edge of the dust component of the disk produces a near-infrared (NIR) excess. The interplay between stars and their disks helps regulate protoplanetary disk evolution and dispersal, which is key to a full understanding of planet formation. To investigate the relations between NIR excess and optical excess in both single and binary stars, we used an archival sample of spectroscopically characterized members of the Taurus star-forming region (τ ∼ 1–2 Myr) with measured luminosities, spectral types, and optical veiling. We combined the archival sample with the Two Micron All Sky Survey and Wide-field Infrared Survey Explorer NIR photometry and high-resolution imaging surveys. We found that NIR and optical excesses are correlated in multiple NIR photometric bands, suggesting that they are closely related, likely because more massive disks have higher inner dust disk walls and are also associated with higher accretion rates. We also found that multiplicity has no impact on accretion or inner disk properties in a sample with a wide range of separations, but the sample was too small to specifically investigate close binaries, where the effects of multiplicity on disk properties should be most significant.

Anisotropic Infall and Substructure Formation in Embedded Disks

Abstract The filamentary nature of accretion streams found around embedded sources suggests that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals that continue to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability. It forms vortices at the inner and outer edges of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of α ∼ 10−2. The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by postprocessing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.

Impact of binary stars on planet statistics – I. Planet occurrence rates and trends with stellar mass

ABSTRACT Close binaries suppress the formation of circumstellar (S-type) planets and therefore significantly bias the inferred planet occurrence rates and statistical trends. After compiling various radial velocity and high-resolution imaging surveys, we determine that binaries with a &amp;lt; 1 au fully suppress S-type planets, binaries with a = 10 au host close planets at 15$_{-12}^{+17}$ per cent the occurrence rate of single stars, and wide binaries with a &amp;gt; 200 au have a negligible effect on close planet formation. We show that F = 43 ± 7 per cent of solar-type primaries in magnitude-limited samples do not host close planets due to suppression by close stellar companions. By removing spectroscopic binaries from their samples, radial velocity surveys for giant planets boost their detection rates by a factor of 1/(1-F) = 1.8 ± 0.2 compared to transiting surveys. This selection bias fully accounts for the discrepancy in hot Jupiter and close Neptune occurrence rates inferred from these two detection methods. Correcting for both planet suppression by close binaries and transit dilution by wide binaries, the occurrence rate of small planets orbiting single G-dwarfs is 2.1 ± 0.3 times larger than the rate inferred from all G-dwarfs in the Kepler survey. Additionally, about half (but not all) of the observed increase in small, short-period planets towards low-mass hosts can be explained by the corresponding decrease in the binary fraction.

The wide-field multiband imaging and slitless spectroscopy survey to be carried out by the Survey Space Telescope of China Manned Space Program

<p indent=0mm>The 2 m-aperture Survey Space Telescope (also known as the China Space Station Telescope, CSST) is a major science project of China Manned Space Program. It is expected to start science operations around 2024 and has a nominal mission lifetime of <sc>10 years.</sc> During observations, CSST will fly independently in the same orbit as the space station while maintaining a large distance apart. It can dock with the space station for refueling and servicing as scheduled or as needed. With a Cook-type three-mirror anastigmat design, CSST can achieve superior image quality within a large field of view (FoV), which gives it an advantage for survey observations. Being an off-axis telescope without any obstruction, its point spread function (PSF) is not affected by diffraction of mirror support structures and is thus helpful for weak-lensing shear measurements. The radius encircling 80% energy of the PSF within CSST’s central 1.1 square degrees of FoV is required to be no more than 0.15″, including all wavefront errors in the optics and instruments and dynamical effects such as the telescope’s attitude control and vibration. CSST will be launched with 5 first-generation instruments including a survey camera, a terahertz receiver, a multichannel imager, an integral field spectrograph, and a cool planet imaging coronagraph. The survey camera is equipped with 30 9k×9k detectors for science observations, each with a filter or grating mounted above, a defocused 9k×9k detector for flux calibration in r band, 8 640×512 near-infrared detectors, fine guide sensors, and wavefront sensors. The primary task of CSST is to carry out a high-resolution large-area multiband imaging and slitless spectroscopy survey covering the wavelength range of <sc>255–1000 nm.</sc> Precision cosmology is the main science driver of the survey, and, therefore, the main area of sky selected for observation is at median-to-high galactic latitude and median-to-high ecliptic latitude. It will take the survey camera roughly <sc>7 years</sc> of operation accumulated over <sc>10 years</sc> of orbital time to image roughly 17500 square degrees of the sky in NUV, u, g, r, i, z, and y bands and take slitless spectroscopy of the same sky in 3 bands. The point-source 5σ limiting magnitudes in g and r bands can reach 26 (AB mag) or higher. The spectral resolution (<italic>R</italic>=<italic>λ</italic>/Δ<italic>λ</italic>) of the slitless spectrograph is specified to be on average no less than 200, and the wide-band-equivalent limiting magnitudes in GV <sc>(400–620 nm)</sc> and GI <sc>(620–1000 nm)</sc> bands will reach 23 or higher. In addition, a number of deep fields will be selected for more observations to reach at least one magnitude deeper than the wide-area survey. The combined advantage of its angular resolution, depth, wavelength range, capability of both imaging and spectroscopy and large-area sky coverage makes the CSST survey highly competitive, and, at the same time, its observations are also highly complementary with other large projects of its time, such as Vera Rubin Observatory, Euclid, and Roman Space Telescope. These projects will provide extremely rich datasets for potential breakthroughs in studies from the solar system to cosmology and beyond.

GravityCam: Wide-field high-resolution high-cadence imaging surveys in the visible from the ground

AbstractGravityCam is a new concept of ground-based imaging instrument capable of delivering significantly sharper images from the ground than is normally possible without adaptive optics. Advances in optical and near-infrared imaging technologies allow images to be acquired at high speed without significant noise penalty. Aligning these images before they are combined can yield a 2.5–3-fold improvement in image resolution. By using arrays of such detectors, survey fields may be as wide as the telescope optics allows. Consequently, GravityCam enables both wide-field high-resolution imaging and high-speed photometry. We describe the instrument and detail its application to provide demographics of planets and satellites down to Lunar mass (or even below) across the Milky Way. GravityCam is also suited to improve the quality of weak shear studies of dark matter distribution in distant clusters of galaxies and multiwavelength follow-ups of background sources that are strongly lensed by galaxy clusters. The photometric data arising from an extensive microlensing survey will also be useful for asteroseismology studies, while GravityCam can be used to monitor fast multiwavelength flaring in accreting compact objects and promises to generate a unique data set on the population of the Kuiper belt and possibly the Oort cloud.

Impact of channel-like erosion patterns on the frequency–magnitude distribution of earthquakes

Reactive flow at depth (either related to underground activities, like enhancement of hydrocarbon recovery and CO2 storage, or to natural flow like in hydrothermal zones) can alter fractures’ topography, which might in turn change their seismic responses. Depending on the flow and reaction rates, instability of the dissolution front can lead to a wormhole-like pronounced erosion pattern. In a fractal structure of rupture process, we question how the perturbation related to well-spaced long channels alters rupture propagation initiated on a weak plane and eventually the statistical feature of rupture appearance in frequency–magnitude distribution (FMD). Contrary to intuition, a spatially uniform dissolution is not the most remarkable case, since it affects all the events proportionally to their sizes leading to a downward translation of FMD: the slope of FMD (b-value) remains unchanged. The parameter–space study shows that the increase of b-value (of 0.08) is statistically significant for optimum characteristics of the erosion pattern with spacing to length ratio of the order of ∼1/40: large-magnitude events are more significantly affected leading to an imbalanced distribution in the magnitude bins of the FMD. The larger the spacing, the lower the channel's influence. Besides, a spatial analysis shows that the local seismicity anomaly concentrates in a limited zone around the channels: this opens perspective for detecting these eroded regions through high-resolution imaging surveys.

High-resolution multispectral satellite image and a postfire ground survey reveal prefire beetle damage on snags in Southern Alaska

Alaskan spruce forests are exposed to both fire and spruce beetles [Dendroctonus rufipennis (Kirby)]. To understand the influence of spruce beetles on the process through which fire affects ecosystem function, we developed a reconstruction technique to measure prefire damage to trees caused by the spruce beetle. We validated our evaluation of prefire tree conditions using a high-resolution multispectral satellite image by comparing our results with a postfire ground survey. The prefire tree conditions determined by the two methods coincided well with each other. This result suggests that combining high-resolution multispectral imaging and postfire ground surveys of spruce beetles on snags is a powerful tool to determine the prefire condition of a forest in a changing boreal forest ecosystem.

THE ASTRALUX LARGE M-DWARF MULTIPLICITY SURVEY

We present the results of an extensive high-resolution imaging survey of M-dwarf multiplicity using the Lucky Imaging technique. The survey made use of the AstraLux Norte camera at the Calar Alto 2.2m telescope and the AstraLux Sur camera at the ESO New Technology Telescope in order to cover nearly the full sky. In total, 761 stars were observed (701 M-type and 60 late K-type), among which 182 new and 37 previously known companions were detected in 205 systems. Most of the targets have been observed during two or more epochs, and could be confirmed as physical companions through common proper motion, often with orbital motion being confirmed in addition. After accounting for various bias effects, we find a total M-dwarf multiplicity fraction of 27+/-3% within the AstraLux detection range of 0.08-6" (semi-major axes of ~3-227 AU at a median distance of 30 pc). We examine various statistical multiplicity properties within the sample, such as the trend of multiplicity fraction with stellar mass and the semi-major axis distribution. The results indicate that M-dwarfs are largely consistent with constituting an intermediate step in a continuous distribution from higher-mass stars down to brown dwarfs. Along with other observational results in the literature, this provides further indications that stars and brown dwarfs may share a common formation mechanism, rather than being distinct populations.

Consideration for a large-scale multi-color imaging and slitless spectroscopy survey on the Chinese space station and its application in dark energy research

Large-scale surveys will be a major effort of the international astronomical community in the next decades. These surveys will produce unprecedentedly large samples with precision measurements and will greatly advance our understanding of fundamental questions of the universe such as dark matter, dark energy, formation and evolution of various astronomical objects. The plan to construct the Chinese space station has brought a rare opportunity for space astronomy in China. Survey observations match well with the operation of the space station, and there has not been a plan for a large-scale high-resolution optical/near UV survey. This can be a unique niche for the astronomy program on board of the Chinese space station and can help China take a leading position in the enterprise of next-generation large-scale surveys. This paper reports the concept of a wide-area high-resolution multiband imaging and slitless spectroscopy survey covering wavelengths from near ultraviolet to near infrared and discusses its application in dark energy research.

Understanding the immediate progenitors of planetary nebulae

AbstractPre-Planetary Nebulae (PPNe) are believed to represent a relatively short, intermediate evolutionary phase in the evolution of AGB stars to Planetary Nebulae (PNe). Our unbiased, high-resolution imaging surveys with HST of young PNe and PPNe show very strong morphological similarities between these classes, enabling us to extend our morphological scheme for PPN classification to young PNe, preserving virtually all of the primary and secondary descriptors, and adding a few new ones. These morphological surveys show that the primary shaping of PNe begins during the PPNe and/or late-AGB phase, and the key to understanding the shaping process lies in the study of these PNe progenitors. Here we present results from two recent studies of PNe progenitors: (i) Hα emission with very broad wings and P-Cygni profiles as probes of the region where the fast post-AGB outflows that do the shaping are most likely launched from, and (ii) equatorial waists with large-sized dust grains and large masses.

Probing Dark Energy with the Kunlun Dark Universe Survey Telescope

ABSTRACTDark energy is an important science driver of many upcoming large-scale surveys. With small, stable seeing, and low thermal infrared background, Dome A, Antarctica, offers a unique opportunity for shedding light on fundamental questions about the universe. We show that a deep, high-resolution imaging survey of 10,000 deg2 in ugrizyJH bands can provide competitive constraints on dark energy equation-of-state parameters using Type Ia supernovae, baryon acoustic oscillations, and weak-lensing techniques. Such a survey may be partially achieved with a coordinated effort of the Kunlun Dark Universe Survey Telescope (KDUST) in yJH bands over 5000–10,000 deg2 and the Large Synoptic Survey Telescope in ugrizy bands over the same area. Moreover, the joint survey can take advantage of the high-resolution imaging at Dome A to further tighten the constraints on dark energy and to measure dark matter properties with strong lensing, as well as galaxy/galaxy weak lensing.

Resolving the L/T transition binary SDSS J2052-1609 AB

Binaries provide empirical key constraints for star formation theories, like the overall binary fraction, mass ratio distribution and the separation distribution. They play a crucial role to calibrate the output of theoretical models, like absolute magnitudes, colors and effective temperature depending on mass, metallicity and age. We present first results of our on-going high-resolution imaging survey of late type brown dwarfs. The survey aims at resolving tight brown dwarf binary systems to better constrain the T dwarf binary fraction. We intent to follow-up the individual binaries to determine orbital parameters. Using NACO at the VLT we performed AO-assisted near-infrared observations of SDSS J2052-1609. High-spatial resolution images of the T1 dwarf were obtained in H and Ks filters. We resolved SDSS J2052-1609 into a binary system with a separation of 0.101" \pm 0.001". Archival data from HST/NICMOS taken one year previous to our observations proves the components to be co-moving. Using the flux ratio between the components we infer J, H and Ks magnitudes for the resolved system. From the near-IR colors we estimate spectral types of T1 +1 -4 and T2.5 \pm 1 for component A and B, respectively. A first estimate of the total system mass yields Mtot > 78 Mjup, assuming a circular orbit.

Direct observation of cosmic strings via their strong gravitational lensing effect – I. Predictions for high-resolution imaging surveys

We use current theoretical estimates for the density of long cosmic strings to predict the number of strong gravitational lensing events in astronomical imaging surveys as a function of angular resolution and survey area. We show that angular resolution is the single most important factor, and that interesting limits on the dimensionless string tension G{mu}/c{sup 2} can be obtained by existing and planned surveys. At the resolution of the Hubble Space Telescope (0'.14), it is sufficient to survey of order a square degree -- well within reach of the current HST archive -- to probe the regime G{mu}/c{sup 2} {approx} 10{sup -8}. If lensing by cosmic strings is not detected, such a survey would improve the limit on the string tension by an order of magnitude on that available from the cosmic microwave background. At the resolution (0'.028) attainable with the next generation of large ground based instruments, both in the radio and the infra-red with adaptive optics, surveying a sky area of order ten square degrees will allow us to probe the G{mu}/c{sup 2} {approx} 10{sup -9} regime. These limits will not be improved significantly by increasing the solid angle of the survey.

A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low-mass initial mass function

Abstract We present the results of a deep wide-field near-infrared survey of 12 deg2 of the Pleiades conducted as part of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high-probability proper motion (PM) members down to 0.03 M⊙ using a combination of UKIDSS photometry and PM measurements obtained by cross-correlating the GCS with data from the Two Micron All Sky Survey, the Isaac Newton Telescope and the Canada–France–Hawaii Telescope. Additionally, we have unearthed 73 new candidate brown dwarf (BD) members on the basis of five-band UKIDSS photometry alone. We have identified 23 substellar multiple system candidates out of 63 candidate BDs from the (Y−K, Y) and (J−K, J) colour–magnitude diagrams, yielding a binary frequency of 28–44 per cent in the 0.075−0.030 M⊙ mass range. Our estimate is three times larger than the binary fractions reported from high-resolution imaging surveys of field ultracool dwarfs and Pleiades BDs. However, it is marginally consistent with our earlier ‘peculiar’ photometric binary fraction of 50 ± 10 per cent presented by Pinfield et al., in good agreement with the 32–45 per cent binary fraction derived from the recent Monte Carlo simulations of Maxted &amp; Jeffries and compatible with the 26 ± 10 per cent frequency recently estimated by Basri &amp; Reiners. A tentative estimate of the mass ratios from photometry alone seems to support the hypothesis that binary BDs tend to reside in near equal-mass ratio systems. In addition, the recovery of four Pleiades members targeted by high-resolution imaging surveys for multiplicity studies suggests that half of the binary candidates may have separations below the resolution limit of the Hubble Space Telescope or current adaptive optics facilities at the distance of the Pleiades (a ∼7 au). Finally, we have derived luminosity and mass functions from the sample of photometric candidates with membership probabilities. The mass function is well modelled by a lognormal peaking at 0.24 M⊙ and is in agreement with previous studies in the Pleiades.

Deficit of Wide Binaries in the η Chamaeleontis Young Cluster

We have carried out a sensitive high-resolution imaging survey of stars in the young (6-8 Myr), nearby (97 pc) compact cluster around η Chamaeleontis to search for stellar and substellar companions. Our data were obtained using the NACO adaptive optics system on the ESO Very Large Telescope (VLT). Given its youth and proximity, any substellar companions are expected to be luminous, especially in the near-infrared, and thus easier to detect next to their parent stars. Here, we present VLT NACO adaptive optics imaging with companion detection limits for 17 η Cha cluster members, and follow-up VLT ISAAC near-infrared spectroscopy for companion candidates. The widest binary detected is ~02, corresponding to the projected separation 20 AU, despite our survey being sensitive down to substellar companions outside 03, and planetary-mass objects outside 05. This implies that the stellar companion probability outside 03 and the brown dwarf companion probability outside 05 are less than 0.16 with 95% confidence. We compare the wide binary frequency of η Cha to that of the similarly aged TW Hydrae association and estimate the statistical likelihood that the wide binary probability is equal in both groups to be less than 2 × 10-4. Even though the η Cha cluster is relatively dense, stellar encounters in its present configuration cannot account for the relative deficit of wide binaries. We thus conclude that the difference in wide binary probability in these two groups provides strong evidence for multiplicity properties being dependent on environment. In two appendices we derive the projected separation probability distribution for binaries, used to constrain physical separations from observed projected separations, and summarize statistical tools useful for multiplicity studies.