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We analyze the photometric data in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) over ∼1200 deg2 to uncover new halo substructures beyond the distance, D ⊙ ∼ 30 kpc, from the Sun. For this purpose, we develop an isochrone filter for an old, metal-poor stellar system to extract the faint main-sequence stars at a range of distances. With this method, we detect not only the previously discovered substructures such as the Orphan Stream, but also a new overdensity toward Boötes at about D ⊙ ∼ 60 kpc and a new stream-like feature toward Pisces at around D ⊙ ∼ 60 kpc. It has been suggested that a small-scale overdensity exists in this direction of Pisces (the so-called Pisces Overdensity), but our results show that the overdensity is widely spread with a tidally elongated feature. Combining our results with the ongoing Hyper Suprime-Cam narrow-band survey and the near-future spectroscopic survey with Prime Focus Spectrograph (PFS) will allow us to place strong constraints on the origin of these halo substructures. [ABSTRACT FROM AUTHOR]

The results of astrometric very long baseline interferometry (VLBI) observations toward an extreme OH/IR star candidate NSV 17351 are presented. Using the VERA (VLBI Exploration of Radio Astrometry) VLBI array , we observed 22 GHz H2O masers of NSV 17351 and derived an annual parallax of 0.247 ± 0.035 mas, which corresponds to a distance of 4.05 ± 0.59 kpc, from the observation. By averaging proper motions of 15 maser spots further, we determined the systemic proper motion of NSV 17351 to be (μαcos δ, μδ)avg. = (−1.19 ± 0.11, 1.30 ± 0.19) mas yr−1. The maser spots spread out over a region of 20 × 30 mas, which can be converted to a spatial distribution of ∼80 × 120 au at the source distance. Internal motions of the maser spots suggest an outward-moving maser region with respect to the estimated position of the central star. From single-dish monitoring of the H2O maser emission, we estimate the pulsation period of NSV 17351 to be 1122 ± 24 d. This is the first report of the periodic activity of NSV 17351, indicating that NSV 17351 could have a mass of ∼4  M ⊙. We confirmed that the time variation of H2O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H2O maser spectra for the last 40 years, we discovered the long-term acceleration in the radial velocity of the circumstellar matter to be 0.17 ± 0.03 km s−1 yr−1. We finally determined the position and kinematics in the Milky Way Galaxy and found that NSV 17351 is located in an interarm region between the Outer and Perseus arms. We note that the astrometric VLBI observation toward extreme OH/IR stars shows us a useful sample of the Galactic dynamics. [ABSTRACT FROM AUTHOR]

Using the Gaia Data Release 2 (DR2) and Early Data Release 3 (EDR3) data and list of post-AGB candidates, we investigate the parallax, proper motion, and binarity for 20 post-AGB stars and candidates that have high radial velocities. From their Gaia distances, their luminosities and kinematics are derived. The evolutionary status of these stars is discussed from their location on the post-AGB evolutionary tracks. Nine stars are confirmed to be post-AGB stars that have initial main-sequence masses of around one or two solar masses. From their kinematics information, two objects among them are identified to belong clearly to the halo population, suggesting low mass. We discuss the origin and evolutionary status of other objects in the sample of this work with high radial velocities. [ABSTRACT FROM AUTHOR]

The membership determination for open clusters in noisy environments of the Milky Way is still an open problem. In this paper, our main aim is to provide the membership probability of stars using proper motions and parallax values of stars using Gaia Third Data Release astrometry. Apart from the Gaia astrometry, we have also used other photometric data sets like the UKIRT Infrared Deep Sky Survey, WISE, the American Association of Variable Star Observers (AAVSO) Photometric All-Sky Survey, and Pan-STARRS1 in order to understand cluster properties from optical to mid-infrared regions. We selected 438 likely members with membership probabilities higher than |$50\%$| and G ≤ 20 mag. We obtained the mean value of proper motion as μ x = 1.27 ± 0.001 and μ y = −0.73 ± 0.002 mas yr−1. The cluster's radius is determined as |${7{^{\prime }_{.}}5}$| (5.67 pc) using radial density profile. Our analysis suggests that NGC 1348 is located at a distance of 2.6 ± 0.05 kpc. The mass function slope is found to be 1.30 ± 0.18 in the mass range 1.0–4.1  M ⊙, which is in fair agreement with Salpeter's value within the 1σ uncertainty. The present study validates that NGC 1348 is a dynamically relaxed cluster. We computed the apex coordinates (A, D) for NGC 1348 as (A °, D °) = (−23.°815 ± 0.°135, −22.°228 ± 0.°105). In addition, calculations of the velocity ellipsoid parameters (VEPs), matrix elements μ ij , direction cosines (lj , mj , nj), and the galactic longitude of the vertex have been conducted in this analysis. [ABSTRACT FROM AUTHOR]

From Gaia DR2 data of eight high-velocity hot post-AGB candidates, LS 3593, LSE 148, LS 5107, HD 172324, HD 214539, LS IV −12 111, LS III +52 24, and LS 3099, we found that six of them have accurate parallaxes which made it possible to derive their distances, absolute visual magnitudes (M V) and luminosity (log  L / L ⊙). All the stars except LS 5107 have an accurate effective temperature (T eff) in the literature. Some of these stars are metal poor, and some of them do not have circumstellar dust shells. In the past, the distances of some stars were estimated to be 6 kpc, which we find to be incorrect. The accurate Gaia DR2 parallaxes show that they are relatively nearby, post-AGB stars. When compared with post-AGB evolutionary tracks we find their initial masses to be in the range 1  M ⊙ to 2  M ⊙. We find the luminosity of LSE 148 to be significantly lower than that of post-AGB stars, suggesting that this is a post-horizontal-branch star or post-early-AGB star. LS 3593 and LS 5107 are new high-velocity hot post-AGB stars from Gaia DR2. [ABSTRACT FROM AUTHOR]

AP Lyn and V837 Her are long-period Mira variable stars in the Milky Way. We performed VLBI Exploration of Radio Astrometry (VERA) phase-referenced observations towards H2O masers associated with AP Lyn and V837 Her. The annual parallaxes of AP Lyn and V837 Her were obtained to be 2.008 ± 0.038 mas and 1.090 ± 0.014 mas, corresponding to distances of 498 ± 10 pc and 917 ± 12 pc, respectively. From our multi-epoch infrared observations using the Kagoshima University 1 m telescope, we derived the mean J -, H -, and K ′-band magnitudes of AP Lyn, V837 Her, and an additional long-period Mira variable BX Cam, whose parallax is known. We derived their pulsation periods to be 433 ± 1 d, 520 ± 1 d, and 458 ± 1 d, respectively, using the K ′-band light curves. The MK –log  P relation of long-period Mira variables seem to be violated by Mira variable stars with larger-than-expected MK values (like OZ Gem) in the Milky Way because of circumstellar extinction leading to an observed dimming effect. AP Lyn, V837 Her, and BX Cam (like OZ Gem) are dimming from the trend to O-rich stars in the Large Magellanic Cloud. This implies that the high metallicity of the Milky Way galaxy increases the opacity of the Mira-type variable stars and strengthens mass loss. [ABSTRACT FROM AUTHOR]

W 48 A core H-2a is one of the young massive protostellar objects in the W 48 region. We conducted multi-epoch astrometric observations of the water (H2O) masers associated with the W 48 A core H-2a with VLBI Exploration of Radio Astrometry (VERA). The trigonometric annual parallax of W 48 A core H-2a was measured to be 0.433 ± 0.026 mas, corresponding to a distance of |$2.31^{+0.15}_{-0.13}$|  kpc. This agrees with the revised parallax of 0.412 ± 0.014 mas by Wu et al. (2019, ApJ, 874, 94). We obtained the systemic proper motion and local standard of rest velocity to be (μαcos δ, μδ) = (0.26 ± 0.73, −3.87 ± 0.33) mas yr−1 and v LSR = 41.9 ± 0.9 km s−1, respectively. The distribution of the H2O masers covers an area of 70 mas × 80 mas, corresponding to 160 au × 180 au at the distance of 2.31 kpc. The internal proper motions of the H2O masers trace an east–west bipolar outflow. With the recent absolute position measurement of the 6.7 GHz methanol (CH3OH) masers and their elliptical distribution, whose major axis is perpendicular to the axis of the bipolar outflow, we suggest the presence of a disk outflow system in core H-2a. The spectral energy distribution (SED) of the driving source of core H-2a was previously reported to yield a luminosity and envelope mass of 8000 ± 1000  |$W_{\odot}$| and 170 ± 30  |$M_{\odot}$|⁠ , respectively. Refitting the SED with the new distance, we obtained the luminosity to be 3100 ± 388  |$L_{\odot}$| and derived the zero age main sequence (ZAMS) stellar mass to be 9 ± 1  |$M_{\odot}$|⁠. Using our distance measurement, we derived the peculiar motion of W 48 A to be (U s, V s, W s) = (1 ± 4, 5 ± 6, −15 ± 5) km s−1. [ABSTRACT FROM AUTHOR]

OZ Geminorum (OZ Gem) is a galactic Mira variable in the Milky Way (MW). We measured its annual parallax with VLBI Exploration of Radio Astrometry to be π = 0.806 ± 0.039 mas, corresponding to a distance of D = 1.24 ± 0.06 kpc. Based on multi-epoch infrared observations with the Kagoshima University 1 m telescope, we also derived the mean J -, H -, and K ′-band magnitudes of OZ Gem to be 5.75 ± 0.47 mag, 4.00 ± 0.16 mag, and 2.65 ± 0.16 mag, respectively. We derived a pulsation period of OZ Gem as 592 ± 1 d from the K ′-band lightcurve. From the period–luminosity (P–L) relation and two-color diagram of the Large Magellanic Cloud (LMC), the property of OZ Gem suggests that OZ Gem is assigned among the carbon-rich Mira variables. However, our optical spectroscopic observational results (with the 1.5 m Kanata telescope) confirmed OZ Gem to be an oxygen-rich Mira star with the detection of multiple titanium oxide transition absorption lines. We suggest that OZ Gem is a low-mass star evolving to an OH/IR star with large mass loss and dust formation. It is predicted that the lower limit to the initial mass of AGB stars for developing the C-rich surface chemistry is larger in the MW than in the LMC because of larger metallicity, and OZ Gem is likely to be the first example to prove this. Our results highlight the necessity of deriving the PL relation of the Milky Way with high accuracy. [ABSTRACT FROM AUTHOR]

We report the results of astrometric VLBI observations toward the Mira variable star BX Cam using the VERA VLBI array. The observation was performed from 2012 February to 2014 November. The parallax obtained is 1.73 ± 0.03 mas corresponding to a distance of 0.58 ± 0.01 kpc. The parallax of this source was reported in Gaia DR2 as 4.13 ± 0.25 mas, and there is a 240% difference between these two measurements. Astrometric results from our VLBI observations show that we exactly traced the angular motions of the seven maser spots in BX Cam. We calculated the stellar luminosities using both parallaxes, and obtained luminosities of |$L_{\ast }^{\mathrm{VERA}} = 4950\pm 170\, L_{\odot }$| and |$L_{\ast }^{\mathrm{Gaia}} = 870\pm 110\, L_{\odot }$|⁠. These deduced luminosities also support the validity of the parallax that we determined with VERA. Evaluating the two parallaxes, we conclude that the parallax of 1.73 ± 0.03 mas from the VERA observations is correct for BX Cam. We obtained the systemic motion of BX Cam as (μαcos δsys, |${\mu }_{\delta }^{\mathrm{sys}}$|⁠) = (13.48 ± 0.14, −34.30 ± 0.18) mas yr−1. The total of 73 H2O maser spots detected from our VLBI observations shows a spatial distribution of 30 au × 80 au, with a strong elongation along the north–south direction. They show outflows with a three-dimensional velocity of 14.79 ± 1.40 km s−1. From a comparison between the time variations of the V -band magnitudes and the H2O masers, we found that the variation of the H2O masers is relevant to that seen in the V band even though the H2O masers do not recover their maximum flux in each cycle. [ABSTRACT FROM AUTHOR]

We present the first measurement of the trigonometric parallax of water masers associated with a Mira star, FV Bootis (FV Boo) using VLBI Exploration of Radio Astrometry (VERA). Based on our multi-epoch VERA observations, we derived the parallax to be 0.97 ± 0.06mas, which corresponds to a distance of 1.03+0.07+0.06 kpc. The water masers around FV Boo were spatially distributed over an area of 41 au x 41 au, and their internal motions indicate the presence of an outflow. Using the Kagoshima University 1 m optical/infrared telescope, we determined the period to be 305.6 d and the mean apparent magnitude to be +2.91 mag in the K'-band. On the period-luminosity plane, the obtained period and K'-band magnitude puts FV Boo slightly below the sequence of Miras, possibly due to circumstellar reddening. Combining our photometric data with COBE and 2MASS datasets spanning over 20 years, we found in the near infrared that FV Boo was significantly fainter in 2005 compared with preceding and later phases. Its color, however, did not show a large variation through this change. We infer that the dimming could be caused by an eclipse due to a cloud in a binary system. [ABSTRACT FROM AUTHOR]

In this paper, we present the distribution of H |$_2$| O masers associated with the semi-regular variable star W Hydrae (W Hya). We have collected the radio interferometric data of the maser distribution taken with the Very Large Array (VLA), the Kashima–Nobeyama InterFErometer (KNIFE), the Multi-Element Radio Link Network (MERLIN), the VLBI Exploration of Radio Astrometry (VERA), and the combined array of the Korean VLBI Network (KVN) and VERA (KaVA) in order to trace the maser distribution variation in two decades. Even though differences in the sensitivities and angular resolutions of the interferometric observations should be taken into account, we attempt to find possible correlation of the maser distribution with the stellar light curve. Our failure in the measurement of the annual parallax of the masers with VERA is likely caused by the properties of the maser features, which have been spatially resolved by the synthesized beam and survived for only half a year or less. No dependence of the maser spot flux density on its size is found in the KNIFE data, suggesting that maser spot size is determined by the physical boundary, as is expected for a clump affected by outward propagation of a stellar pulsation shock wave, rather than the (spherical) geometry of maser beaming in the maser gas clump. [ABSTRACT FROM AUTHOR]

As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151 ± 0.042 mas, which corresponds to a distance of |$D = 6.61^{+2.55}_{-1.44}\:{\rm kpc}$|⁠ , and the obtained proper motion components were |$(\mu _\alpha {\rm cos}\delta ,\, \mu _\delta) = (-1.44 \pm 0.15,\, -0.27 \pm 0.16)\:{\rm mas\:yr^{-1}}$| in equatorial coordinates. Assuming Galactic constants of |$(R_0,\, \Theta _0) = (8.05 \pm 0.45\:{\rm kpc},\, 238 \pm 14\:{\rm km\:s^{-1}})$|⁠ , the Galactocentric distance and rotation velocity were measured to be |$(R,\, \Theta) = (13.04 \pm 2.24\:{\rm kpc},\, 239 \pm 22\:{\rm km\:s^{-1}})$|⁠ , which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, |$L_{\rm Bol} = (3.11 \pm 2.86) \times 10^{3}\, L_{\odot }$|⁠ , which corresponds to a spectral type of B1–B2. Analysis of |${}^{12}{\rm{CO}}$| (J = 1–0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which matches well a structure predicted by numerical simulation of the cloud–cloud collision phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of the two initial clouds was as slow as 3– |$5\:{\rm km\, s^{-1}}$|⁠ , which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (∼3–5 km s−1), as suggested by Takahira, Tasker, and Habe (2014 , ApJ, 792, 63). [ABSTRACT FROM AUTHOR]

Using the VLBI Exploration of Radio Astrometry (VERA), we measured the trigonometric parallax of an H2O maser source in a variable star of Mira Cet type, Y Lib, to be 0.855 ± 0.050 mas, corresponding to a distance of 1.17 ± 0.07 kpc. From multi-epoch infrared observations with the Kagoshima University 1 m telescope, we derived the mean J , H , and K ′-band magnitudes of Y Lib to be 4.34 ± 0.22 mag, 3.62 ± 0.18 mag, and 3.25 ± 0.16 mag, respectively. The pulsation period of Y Lib was obtained to be 277.2 ± 13.9 d. We derived the effective temperature and radius of Y Lib to be 3100 ± 125 K and |$211 \pm 11 \, R_{\odot }$|⁠ , respectively. The peculiar motion of Y Lib U s (motion towards the Galactic center), V s (motion in the direction of Galactic rotation), and W s (motion towards the Galactic North Pole) were obtained to be −16 ± 3 km s−1, 25 ± 2 km s−1, and 13 ± 3 km s−1, respectively. After validation, we used the new release of the GALactic ORbit simulation package to trace the past 1 Gyr orbit of Y Lib in the Milky Way. Fitting the orbit of Y Lib with the MWPotential2014 Galactic Potential model produced high eccentricity in the direction perpendicular to the Galactic center, but decreasing the Miyamoto–Nagai disk potential contribution in the Milky Way model produced a reasonable result of the Y Lib orbit. [ABSTRACT FROM AUTHOR]

We report the results of the measurement of the trigonometric parallax of an H2O maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be 0.314 ± 0.070 mas, corresponding to a distance of $3.18^{+0.90}_{-0.66}\,{\rm kpc}$. Our results confirm IRAS 22555+6213 to be located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to be (Usrc, Vsrc, Wsrc) = (4 ± 4, −32 ± 6, 8 ± 6) km s−1, where Usrc, Vsrc, and Wsrc are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC 7538, and Cepheus A lie along the same line of sight, and are within 2° on the sky. Their parallax distances, with which we derived their absolute position in the Milky Way, show that IRAS 22555+6213 and NGC 7538 are associated with the Perseus Arm, while Cepheus A is located in the Local Arm. We compared the kinematic distances of IRAS 22198+6336, G108.18+05.51, G108.20−00.58, G108.47+02.81, G108.59+00.49, Cepheus A, NGC 7538, G111.23−01.23, G111.25−00.76, and IRAS 22555+6213 derived with flat and non-flat rotation curves with their parallax distance and found the kinematic distance derived from the non-flat rotation assumption (−5 to −39 km s−1 lag) to be consistent with the parallax distance. [ABSTRACT FROM AUTHOR]

Multiepoch phase-referencing VLBI (Very Long Baseline Interferometry) observations with VERA (VLBI Exploration of Radio Astrometry) were performed for the symbiotic star R Aquarii (R Aqr) from 2005 September to 2006 October. Tracing one of the v = 2, J = 1–0 SiO maser spots, we measured an annual parallax of π = 4.59 ± 0.24 mas, corresponding to a distance of $218_{-11}^{+12}\:$pc. Our result is consistent with earlier distance measurements, but yields the highest accuracy of ∼ 5% level. Applying our distance, we derived an absolute K-band magnitude of MK = −7.71 ± 0.11, which is consistent with the recent period–luminosity relation by VLBI parallax measurements for five OH-Mira variables. In addition, the expansion age of an inner nebula around R Aqr is found to be ∼ 240 yr, corresponding to about the year 1773. [ABSTRACT FROM PUBLISHER]