Outermost Disk Research Articles

The TYPHOON Stellar Population Synthesis Survey. I. The Young Stellar Population of the Great Barred Spiral NGC 1365

We analyze TYPHOON long-slit-absorption line spectra of the starburst barred spiral galaxy NGC 1365 obtained with the Progressive Integral Step Method covering an area of 15 kpc2. Applying a population synthesis technique, we determine the spatial distribution of ages and metallicities of the young and old stellar populations together with star formation rates, reddening, extinction, and the ratio R V of extinction to reddening. We detect a clear indication of inside-out growth of the stellar disk beyond 3 kpc characterized by an outward increasing luminosity fraction of the young stellar population, a decreasing average age, and a history of mass growth, which was finished 2 Gyr later in the outermost disk. The metallicity of the young stellar population is clearly super solar but decreases toward larger galactocentric radii with a gradient of −0.02 dex kpc−1. On the other hand, the metal content of the old population does not show a gradient and stays constant at a level roughly 0.4 dex lower than that of the young population. In the center of NGC 1365, we find a confined region where the metallicity of the young population drops dramatically and becomes lower than that of the old population. We attribute this to the infall of metal-poor gas, and additionally, to interrupted chemical evolution where star formation is stopped by active galactic nuclei and supernova feedback and then after several gigayears resumes with gas ejected by stellar winds from earlier generations of stars. We provide a simple model calculation as support for the latter.

Carbon Stars as Standard Candles: An Empirical Test for the Reddening, Metallicity, and Age Sensitivity of the J-region Asymptotic Giant Branch (JAGB) Method

The J-region Asymptotic Giant Branch (JAGB) method is a standard candle based on the intrinsic luminosities of carbon stars in the near-infrared. We directly constrain the impact of metallicity, age, and reddening on the JAGB method. We assess how the mode, skew, and spread of the JAGB star LF change throughout diverse stellar environments in M31's NE disk from 13 < d < 18 kpc using data from the Panchromatic Hubble Andromeda Treasury (PHAT). As expected, the mode is found to be fainter in higher-reddening regions. To cross-check this result, we also measure a fiducial J-band ground-based JAGB distance using data from the UKIRT/WFCam in M31's outermost disk (18 < d < 40 kpc) where internal reddening is minimal. We find that this J-band distance modulus agrees well with the F110W distance moduli measured in the lowest-reddening regions of the PHAT data, demonstrating the JAGB method is most accurate if measured in the low-reddening outer disks of galaxies. On the other hand, the mode of the JAGB star LF appears empirically to show no dependence on age or metallicity within the range −0.18 < [M/H] < −0.26 dex. In conclusion, the JAGB method proves to be a robust standard candle capable of calibrating the luminosities of Type Ia supernovae and therefore providing a high-accuracy, high-precision measurement of the Hubble constant.

Improving the Design of the Disc Harrow for Berry Plantations

Introduction. Reducing the distance of throwing soil into the zone around bushes and maintaining a leveled surface between rows of berry crops are urgent scientific problems. Aim of the Article. To identify the basic parameters for the interaction of a spherical disk with waterlogged soil and on this basis to develop the technical solution for reducing the distance of soil throwing away in space between rows of berry crops. Materials and Methods. The object of research is an orchard disc harrow equipped with a protective shield mounted in front of the outermost disc of the tool front panel. The subject of the research is the process of interaction of the end disc of the front harrow plate with the waterlogged soil in berry plantations. The length of the protective shield and its spatial orientation were chosen as optimization parameters for field experiments. The quality evaluation of intertillage of the berry plantations was carried out by profiling their surfaces. Results. Based on the results of theoretical studies, it was found that the angle of inclination of the protective shield in the horizontal plane should be within 53–54°, and with respect to the movement of the harrow – 50–58°. The results of field experiments have confirmed the theoretical conclusions. It has been established that only a protective shield, the length of which is 450 mm and the installation angle of 50°, allows completely eliminating the side throw of the soil beyond the width of the tool. In addition, these parameters ensure the stable operation of the disc tool in almost any soil moisture and weed infestation of space between berry bushes. Discussion and Conclusion. The use of a modernized tillage tool made it possible to exclude the soil throwing into the bush zone to increase the speed of the unit by 25%.

Advantages of the aerodynamic performance of micro‐Tesla turbines

AbstractTesla turbines, featuring bladeless turbomachinery and energy transformation using the viscosity of the working medium, have wide application prospects in renewable energy utilization as micropower equipment and portable power units and show better aerodynamic performance with a smaller turbine size. In this paper, a miniaturization method of Tesla turbines, including the stator and rotor, was proposed based on its sensitivity analysis results and flow similitude law. A typical Tesla turbine with a disc outer diameter of 100 mm was miniaturized to 50, 20, and 10 mm, respectively. In addition, the miniaturized Tesla turbines, including both the simplified single‐channel turbine model and the multichannel turbine model used in practical applications, were simulated numerically. The results show that the miniaturization method that maintains the two high‐impact dimensionless parameters at their optimal values is simple, reasonable, and effective. The isentropic efficiency of the single‐channel Tesla turbine decreases slightly with its scaling down. However, for the multichannel Tesla turbine in practical applications, the isentropic efficiency increases significantly with a decrease in turbine size, due to a decrease in the impact of the outermost disc channel on the flow fields of the inner disc channels (called the casing wall effect). This is embodied by the phenomenon that part of the working medium in the inner disc channels flows into the outermost disc channel through the nozzle‐rotor chamber, and the proportion of this part of the working medium decreases significantly with a decrease in turbine size. In conclusion, the Tesla turbine with a smaller turbine size exhibits better aerodynamic performance and has great potential in the field of microturbomachinery.

Quantifying Chemical and Kinematical Properties of Galactic Disks

Abstract We aim to quantify the chemical and kinematical properties of Galactic disks with a sample of 119,558 giant stars having abundances and 3D velocities taken or derived from the APOGEE DR17 and Gaia EDR3 catalogs. A Gaussian mixture model is employed to distinguish the high-α and low-α sequences along the metallicity by simultaneously using chemical and kinematical data. Four disk components are identified and quantified; they are named the hαmp, hαmr, lαmp, and lαmr disks and correspond to the high-α or low-α, and metal-poor or metal-rich properties. Combined with the spatial and stellar-age information, we confirm that they are well interpreted by the two-infall formation model. The first infall of turbulent gas quickly forms the hot and thick hαmp disk with consequent thinner hαmr and lαmr disks. Then the second gas accretion forms a thinner and outermost lαmp disk. We find that the inside-out and upside-down scenario does not only satisfy the overall Galactic disk formation of these two major episodes but is also presented in the formation sequence of the three inner disks. Importantly, we reveal the inverse age–[M/H] trend of the lαmr disk, which means its younger stars are more metal-poor, indicating that the rejuvenated gas from the second accretion gradually dominates later star formation. Meanwhile, the recently formed stars converge to [M/H] ∼ −0.1 dex, demonstrating a sufficient mixture of gas from two infalls.

An Atacama Large Millimeter/submillimeter Array Survey of Chemistry in Disks around M4–M5 Stars

Abstract M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an Atacama Large Millimeter/submillimeter Array survey of molecular line emission toward a sample of five protoplanetary disks around M4–M5 stars (FP Tau, J0432+1827, J1100-7619, J1545-3417, and Sz 69). These observations can resolve chemical structures down to tens of astronomical units. Molecular lines of 12CO, 13CO, C18O, C2H, and HCN are detected toward all five disks. Lines of H2CO and DCN are detected toward 2/5 and 1/5 disks, respectively. For disks with resolved C18O, C2H, HCN, and H2CO emission, we observe substructures similar to those previously found in disks around solar-type stars (e.g., rings, holes, and plateaus). C2H and HCN excitation conditions estimated interior to the pebble disk edge for the bright disk J1100-7619 are consistent with previous measurements around solar-type stars. The correlation previously found between C2H and HCN fluxes for solar-type disks extends to our M4–M5 disk sample, but the typical C2H/HCN ratio is higher for the M4–M5 disk sample. This latter finding is reminiscent of the hydrocarbon enhancements found by previous observational infrared surveys in the innermost (&lt;10 au) regions of M-star disks, which is intriguing since our disk-averaged fluxes are heavily influenced by flux levels in the outermost disk, exterior to the pebble disk edge. Overall, most of the observable chemistry at 10–100 au appears similar for solar-type and M4–M5 disks, but hydrocarbons may be more abundant around the cooler stars.

Spectroscopy of the helium-rich binary ES Ceti reveals accretion via a disc and evidence of eclipses

Context. Amongst the hydrogen-deficient accreting binaries known as the AM CVn stars are three systems with the shortest known orbital periods: HM Cnc (321 s), V407 Vul (569 s), and ES Cet (620 s). These compact binaries are predicted to be strong sources of persistent gravitational wave radiation. HM Cnc and V407 Vul are undergoing direct impact accretion in which matter transferred from their donor hits the accreting white dwarfs directly. ES Cet has the longest period of the three and is amongst the most luminous AM CVn stars, but it is not known whether it accretes via a disc or direct impact. ES Cet displays strong HeII 4686 line emission, which is sometimes a sign of magnetically controlled accretion. Peculiarly, although around one third of hydrogen accreting white dwarfs show evidence of magnetism, none have been found amongst helium accretors. Aims. We present the results of Magellan and VLT spectroscopic and spectropolarimetric observing campaigns dedicated to ES Cet with the aim of understanding its accretion structure. Methods. Based on the data collected, we derived trailed spectra, computed Doppler maps of the emission lines, and looked for circular polarisation and variability. Results. We find strong variability in our spectra on the 620 s period. The lines show evidence of double-peaked emission, characteristic of an accretion disc, with an additional component associated with the outermost disc, rather than a direct impact, which is broadly consistent with S-wave emission from the gas stream or disc impact region. This confirms beyond any doubt that 620 s is the orbital period of ES Cet. We find no significant circular polarisation (below 0.1%). The trailed spectra show that ES Cet’s outer disc is eclipsed by the mass donor, revealing at the same time that the photometric minimum coincides with the hitherto unrecognised eclipse. Conclusions. ES Cet shows spectroscopic behaviour consistent with accretion via a disc, and is the shortest orbital-period eclipsing AM CVn star known.

Multi-wavelength photometry during the 2018 superoutburst of the WZ Sge-type dwarf nova EG Cancri

Abstract We report on the multi-wavelength photometry of the 2018 superoutburst in EG Cnc. We have detected stage A superhumps and long-lasting late-stage superhumps via the optical photometry and have constrained the binary mass ratio and its possible range. The median value of the mass ratio is 0.048 and the upper limit is 0.057, which still implies that EG Cnc is one of the possible candidates for period bouncers. This object also showed multiple rebrightenings in this superoutburst which are the same as those in its previous superoutburst in 1996–1997, despite the difference in the main superoutburst. This would represent that the rebrightening type is inherent to each object and is independent of the initial disk mass at the beginning of superoutbursts. We also found that B − I and J − Ks colors were unusually red just before the rebrightening phase and became bluer during the quiescence between rebrightenings, which would mean that the low-temperature mass reservoir at the outermost disk accreted with time after the main superoutburst. Also, the ultraviolet flux was sensitive to rebrightenings as well as the optical flux, and the U − B color became redder during the rebrightening phase, which would indicate that the inner disk became cooler when this object repeated rebrightenings. Our results thus basically support the idea that the cool mass reservoir in the outermost disk is responsible for rebrightenings.

A Redshifted Inner Disk Atmosphere and Transient Absorbers in the Ultracompact Neutron Star X-Ray Binary 4U 1916–053

Abstract The very small accretion disks in ultracompact X-ray binaries are special laboratories in which to study disk accretion and outflows. We report on three sets of new (250 ks total) and archival (50 ks) Chandra/HETG observations of the “dipping” neutron star X-ray binary 4U 1916–053, which has an orbital period of P ≃ 50 minutes. We find that the bulk of the absorption in all three spectra originates in a disk atmosphere that is redshifted by v ≃ 220–290 km s−1, corresponding to the gravitational redshift at a radius of R ∼ 1200 GM/c 2. This shift is present in the strongest, most highly ionized lines (Si xiv and Fe xxvi), with a significance of 5σ. Absorption lines observed during dipping events (typically associated with the outermost disk) instead display no velocity shifts and serve as a local standard of rest, suggesting that the redshift is intrinsic to an inner disk atmosphere and not due to radial motion in the galaxy or a kick. In two spectra, there is also evidence of a more strongly redshifted component that would correspond to a disk atmosphere at R ∼ 70 GM/c 2; this component is significant at the 3σ level. Finally, in one spectrum, we find evidence of a disk wind with a blueshift of . If real, this wind would require magnetic driving.

Expression pattern of candidate genes in early capitulum morphogenesis of Chrysanthemum lavandulifolium

The understanding of capitulum morphogenesis is critical for modification of chrysanthemum flower type. Previous studies showed candidate genes which involved in the inflorescence architecture, such as PIN-FORMED 1 (PIN1), AUXIN RESPONSE FACTOR 5 (ARF5) and LEAFY (LFY), acted dominant role during early flower development. However, it is not known whether those candidate genes play parts in the capitulum morphogenesis. In the present study, floral morphogenesis and the corresponding external morphological changes in Chrysanthemum lavandulifolium were observed using scanning electron microscope and light microscope technology. Capitulum morphogenesis showed that ray florets primordia initiated later than the outermost disc florets primordia at the middle stage of florets primordia differentiation (stage 6), breaking the acropetal initiation of organ primordia on capitulum. Organogenesis of disc and ray florets showed that the early generation of florets corollas primordia was the key differentiation stages, in which disc and ray florets fused with actinomorphic and zygomorphic corollas, respectively. Furthermore, the expression patterns of inflorescence architecture related genes were detected at key stages of capitulum morphogenesis as well as the different organs on capitulum using quantitative real time PCR (qRT-PCR). The transcripts of ClARF5 specially increased at stage 5 and stage 6, as well as in ray florets corollas. The results indicated that ClARF5 might be responsible for the orientation and initiation of disc and ray florets during early capitulum morphogenesis. Studies on the capitulum morphogenesis of C. lavandulifolium not only bring molecular insights into capitulum morphogenesis, but also lay foundation for the flower type-oriented modification in cultivated chrysanthemums.

Radial Velocities in the Outermost Disk toward the Anticenter

Abstract We measure the mean Galactocentric radial component of the velocity of stars (v R ) in the disk at 8 kpc &lt; R &lt; 28 kpc in the direction of the anticenter. For this, we use the Apache Point Galactic Evolution Experiment. Furthermore, we compare the result with H i maps along the same line of sight. We find an increase in positive (expansion) v R at R ≈ 9–13 kpc, reaching a maximum of ≈6 km s−1, and a decrease at large values of R, reaching a negative (contraction) value of ≈−10 km s−1 for R &gt; 17 kpc. Negative velocities are also observed in 21 cm H i maps, possibly dominated by local gas emission. Among the possible dynamical causes for these non-zero v R , factors such as the effect of the Galactic bar, streams, or mergers do not seem appropriate to explain our observations. An explanation might be the gravitational attraction of overdensities in a spiral arm. As a matter of fact, we see a change of regime from positive to negative velocities around R ≈ 15 kpc, in the position where we cross the Outer spiral arm in the anticenter. The mass in spiral arms necessary to produce these velocities would be about 3% of the mass of the disk, consistent with our knowledge of the spiral arms. Another scenario that we explore is a simple class of out-of-equilibrium systems in which radial motions are generally created by the monolithic collapse of isolated self-gravitating overdensities.

Weak reducing disks and disk surgery

Let [Formula: see text] be an unknot in [Formula: see text]-bridge position in the [Formula: see text]-sphere. We give an example of a pair of weak reducing disks [Formula: see text] and [Formula: see text] for [Formula: see text] such that both disks obtained from [Formula: see text] ([Formula: see text]) by a surgery along any outermost disk in [Formula: see text], cut off by an outermost arc of [Formula: see text] in [Formula: see text], are not weak reducing disks, i.e. the property of weak reducibility of compressing disks is not preserved by a disk surgery.

Dark Memories of the Past: Discovery of Ultra-Diffuse Objects around NGC 1068

AbstractWe have searched for a sign of the past dynamical disturbance events on NGC 1068, an archetypical Type-2 Seyfert galaxy, using deep and wide optical imaging data by the Subaru telescope. The data taken by Hyper Suprime-Cam (HSC) as well as the archived data by Suprime-Cam reveal several faint outer structures of the galaxy, most of which were never reported before. We discover three large (re = 3 -5.5 kpc), extremely diffuse objects (UDOs) within 45 kpc from the center of NGC 1068. We suggest that two of these UDOs are actually a part of a large loop-like structure surrounding NGC 1068. Such an extremely faint loop or stream is the direct evidence for a past minor merger event. The third UDO has a distorted morphology, suggesting that it is under the influence of strong tidal field. Furthermore, we have identified another ultra-diffuse but compact (μ0,r &gt; 25 mag arcsec-2, re ~ 0.8kpc) dwarf galaxy within ~140 kpc from NGC 1068. We speculate that this ultra-diffuse dwarf could be the object related to the ancient tidal disruption event (tidal dwarf) during the early mass assembly period of NGC 1068. We also detect an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are also expected to arise in a late phase (up to several billion years ago) of a minor merger, according to numerical simulations. Our findings are consistent with the idea that the AGN activity in NGC 1068 is caused by a past minor merger.

New Constraints on Turbulence and Embedded Planet Mass in the HD 163296 Disk from Planet–Disk Hydrodynamic Simulations

Abstract Recent Atacama Large Millimeter and Submillimeter Array (ALMA) observations of the protoplanetary disk around the Herbig Ae star HD 163296 revealed three depleted dust gaps at 60, 100, and 160 au in the 1.3 mm continuum as well as CO depletion in the middle and outer dust gaps. However, no CO depletion was found in the inner dust gap. To examine the planet–disk interaction model, we present results of 2D two fluid (gas + dust) hydrodynamic simulations coupled with 3D radiative transfer simulations. To fit the high gas-to-dust ratio of the first gap, we find that the Shakura–Sunyaev viscosity parameter α must be very small ( ) in the inner disk. On the other hand, a relatively large α ( ) is required to reproduce the dust surface density in the outer disk. We interpret the variation of α as an indicator of the transition from an inner dead zone to the outer magnetorotational instability (MRI) active zone. Within ∼100 au, the HD 163296 disk’s ionization level is low, and non-ideal magnetohydrodynamic effects could suppress the MRI, so the disk can be largely laminar. The disk’s ionization level gradually increases toward larger radii, and the outermost disk ( au) becomes turbulent due to MRI. Under this condition, we find that the observed dust continuum and CO gas line emissions can be reasonably fit by three half-Jovian-mass planets (0.46, 0.46, and ) at 59, 105, and 160 au, respectively.

Full-Scale Rotary Cutting Test to Study the Influence of Disc Cutter Installment Radius on Rock Cutting Forces

Disc cutters mounted on the cutterhead of tunnel boring machine (TBM) can be divided into center cutter, face cutter and gauge cutter according to their installment radius. Due to the differences in rock cutting condition, disc cutter turning radius and cutterhead stiffness distribution, they show very different characteristics in the magnitude of disc cutter normal and rolling forces. For the realistic modeling of whole cutterhead, full-scale rotary cutting test using disc cutter with different installment radius is a useful and inspiring way to study the influence of disc cutter installment radius on rock cutting forces. By conducting full-scale rotary cutting test, two main conclusions are obtained. First, disc cutter normal and rolling forces both decrease rapidly and then remain nearly stable when disc cutter installment radius increases. Second, the normal and rolling forces of the innermost disc cutters are two to four times higher than those of the outermost disc cutters. This study verifies the very uneven distribution of the disc cutter cutting forces on the cutterhead, and it can contribute to better arrangement of the disc cutters to ensure that they subject to similar loading and wear conditions and also can offer suggestions for field TBM operation to avoid severe overloading of the inner disc cutters.

Morphological evidence for a past minor merger in the Seyfert galaxy NGC 1068

Abstract Deep optical imaging with both Hyper Suprime-Cam and Suprime-Cam on the 8.2 m Subaru Telescope reveals a number of outer faint structures around the archetypical Seyfert galaxy NGC 1068 (M 77). We find three ultra diffuse objects (UDOs) around NGC 1068. Since these UDOs are located within the projected distance of 45 kpc from the center of NGC 1068, they appear to be associated with NGC 1068. Hereafter, we call them UDO-SW, UDO-NE, and UDO-SE where UDO = Ultra Diffuse Object, SW = southwest, NE = northwest, and SE = southeast; note that UDO-SE was already found in the SDSS Stripe 82 data. Among them, UDO-NE and UDO-SW appear to be a part of a loop or stream structure around the main body of NGC 1068, providing evidence for the physical connection to NGC 1068. We consider that UDO-SE may be a tidal dwarf galaxy. We also find another UDO-like object that is two magnitudes fainter and smaller by a factor of 3 to 5 than those of the three UDOs. This object may belong to a class of low surface brightness galaxy. Since this object is located along the line connecting UDO-NE and UDO-SW, it is suggested that this object is related to the past interaction event that formed the loop by UDO-NE and UDO-SW, thus implying the physical connection to NGC 1068. Another newly discovered feature is an asymmetric outer one-arm structure emanating from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are expected to arise in a late phase of a minor merger, according to published numerical simulations of minor mergers. All these lines of evidence show that NGC 1068 experienced a minor merger several billion years ago. We then discuss the minor-merger driven triggering of nuclear activity in the case of NGC 1068.

LUNAR VOLATILE DEPLETION DUE TO INCOMPLETE ACCRETION WITHIN AN IMPACT-GENERATED DISK.

The Moon may have formed from an Earth-orbiting disk of vapor and melt produced by a giant impact.1 The Moon and Earth's mantles have similar compositions. However, it is unclear why lunar samples are more depleted in volatile elements than terrestrial mantle rocks2-3, given that an evaporative escape mechanism4 appears inconsistent with expected disk conditions.5 Dynamical models6-7 suggest that the Moon initially accreted from the outermost disk, but later acquired up to 60% of its mass from melt originating from the inner disk. Here we combine dynamical, thermal and chemical models to show that volatile depletion in the Moon can be explained by preferential accretion of volatile-rich melt in the inner disk to the Earth, rather than to the growing Moon. Melt in the inner disk is initially hot and volatile-poor, but volatiles condense as the disk cools. In our simulations, the delivery of inner disk melt to the Moon effectively ceases when gravitational interactions cause the Moon's orbit to expand away from the disk, and this termination of lunar accretion occurs prior to condensation of potassium and more volatile elements. Thus, the portion of the Moon derived from the inner disk is expected to be volatile depleted. We suggest that this mechanism may explain part or all of the Moon's volatile depletion, depending on the degree of mixing within the lunar interior.

Behind the diversity: Ontogenies of radiate, disciform, and discoid capitula of Chrysanthemum and its allies

AbstractAsteraceae are distinguishable by their head‐like inflorescence called a capitulum. There are a variety of capitulum types due to different combinations of different composing florets. Morphological evolution of capitula must involve homoplasy under selective constraints. Therefore, a comparative examination of ontogenies of divergent capitula among phylogenetically close taxa is important to investigate the genetic and molecular bases of this trait. In the subtribe Artemisiinae, tribe Anthemideae, three closely related genera have different flower heads: Chrysanthemum with the radiate, Ajania with the disciform, and Stilpnolepis with the discoid capitula. Through observations using scanning electron microscopy, we examined the morphogenetic processes of flower heads of representative species of these genera. The morphological differentiation of the discoid from the radiate/disciform capitula occurred early in the floral initiation stage. The development of the ray/marginal florets of the radiate/disciform capitula lagged behind the outermost disc florets throughout the phases of floral initiation and floral organogenesis. Primordia of their 1–2 dorsal corolla lobes and all stamens ceased to grow soon after initiation. In contrast, all florets on a discoid capitulum developed equally in rates and modes into bisexual actinomorphic flowers. Differentiation between the radiate and the disciform capitula occurred late during the floral maturation stage. Our data provided evidence to the interpretation that uniformly acropetal development only occurs in species with homogamous flower heads, and to the idea that the timing of ontogenetic divergence between taxa is positively correlated with the phylogenetic distance of the taxa.

FIRST DETECTION OF [C I] 3 P 1 – 3 P 0 EMISSION FROM A PROTOPLANETARY DISK

We performed single point [C I] $^3$P$_1$-$^3$P$_0$ and CO J=4-3 observations toward three T Tauri stars, DM Tau, LkCa 15, and TW Hya, using the Atacama Large Millimeter/submillimeter Array (ALMA) Band 8 qualification model receiver installed on the Atacama Submillimeter Telescope Experiment (ASTE). Two protostars in the Taurus L1551 region, L1551 IRS 5 and HL Tau, were also observed. We successfully detected [C I] emission from the protoplanetary disk around DM Tau as well as the protostellar targets. The spectral profile of the [C I] emission from the protoplanetary disk is marginally single-peaked, suggesting that atomic carbon (C) extends toward the outermost disk. The detected [C I] emission is optically thin and the column densities of C are estimated to be <~10$^{16}$ cm$^{-2}$ and ~10$^{17}$ cm$^{-2}$ for the T Tauri star targets and the protostars, respectively. We found a clear difference in the total mass ratio of C to dust, $M$(C)/$M$(dust), between the T Tauri stars and protostellar targets; the $M$(C)/$M$(dust) ratio of the T Tauri stars is one order of magnitude smaller than that of the protostars. The decrease of the estimated $M$(C)/$M$(dust) ratios for the disk sources is consistent with a theoretical prediction that the atomic C can survive only in the near surface layer of the disk and C$^+$/C/CO transition occurs deeper into the disk midplane.

A PILOT STUDY USING DEEP INFRARED IMAGING TO CONSTRAIN THE STAR FORMATION HISTORY OF THE XUV STELLAR POPULATIONS IN NGC 4625

In a LCDM universe, disk galaxies' outer regions are the last to form. Characterizing their contents is critical for understanding the ongoing process of disk formation, but observing outer disk stellar populations is challenging due to their low surface brightness. We present extremely deep 3.6 micron observations (Spitzer IRAC) of NGC 4625, a galaxy known for its radially extended ultraviolet emitting stellar population. We combine the new imaging with archival UV imaging from the GALEX mission to derive multiwavelength radial profiles for NGC 4625 and compare them to stellar populations models. The colors can be explained by the young stellar population that is responsible for the UV emission and indicate that the current star formation rates in the outermost disk are recent. Extended star formation in NGC 4625 may have been initiated by an interaction with neighboring galaxies NGC 4618 and NGC 4625a, supporting speculation that minor interactions are a common trigger for outer disk star formation and late stage disk growth.