 Subjects -> ASTRONOMY (Total: 94 journals)
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- Optical spectroscopic observations of a symbiotic star MWC 560 in the mass
accumulation phase
Authors: Ando K; Fukuda N, Sato B, et al.
Abstract: AbstractThere are about a dozen symbiotic stars known to produce high-velocity jets during outbursts. MWC 560 (V694 Mon) is a symbiotic star that seems to show a permanent jet. After showing an unexpected brightening in 2018 November, it has continued to brighten until 2021 and is currently in the brightest state ever. We have been conducting long-term high-dispersion spectroscopic monitoring of this object since 2016 March. An emission wing with vFWHM ≈ 700 km s−1 in the hydrogen Balmer line at an unexpected brightening event in 2018 was reported by Ando et al. (2021, PASJ, 73, L1). In subsequent continuous observations, this emission wing was no longer seen on 2019 February 6. The absorption lines seen in the hydrogen Balmer lines are gradually deepening and spreading to the slower side of the velocity, and the outflow velocity is becoming slower. The expanding component generated by the outburst was initially observed in the emission wing just after the 2018 outburst, got gradually cooler, and was observed in the absorption line after 2019.
PubDate: Sat, 13 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab104
Issue No: Vol. 73, No. 6 (2021)
- Analyses of a datable solar eclipse record in Maya Classic period
monumental inscriptions
Authors: Hayakawa H; Sôma M, Kinsman J.
Abstract: ABSTRACTHistorical records of total solar eclipses provide vital information for computing the rotation of the Earth and understanding its long-term variations in the time before modern measurements. While eclipses recorded around Eurasia and North Africa for millennia have been subjected to consideration in this context, eclipse records in the American continents have received little attention. In this study, we analysed the solitary observational record for a solar eclipse conducted by the ancient Maya on 790 July 16 in the Julian calendar, recorded on the Stela 3 of Santa Elena Poco Uinic (N16°35′, W91°44′). This stela has an eclipse glyph and is associated with a total solar eclipse. Taking the up-to-date Earth rotation (ΔT) rate into account, our calculations locate this site slightly out of the totality path. The visibility of the total solar eclipse from Santa Elena Poco Uinic would require ΔT to be 4074 s < ΔT < 4873 s. In comparison with the contemporary eclipse records, this yields a short-term increase in ΔT ≥ 800 s between 761 and 790 and a decrease in ΔT ≥ 580 s between 790 and 873. Therefore, the total solar eclipse on 790 July 16 cannot be expected to have been visible from Santa Elena Poco Uinic, unlike what has been previously considered. We conclude that this stela probably records a partial solar eclipse of great magnitude (≈0.946) visible under favourable meteorological conditions or is based on hearsay from the southern coastal area.
PubDate: Wed, 20 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab088
Issue No: Vol. 73, No. 6 (2021)
- High-energy gamma-rays and neutrons observed in very impulsive solar flare
on 2012 June 3
Authors: Kamiya K; Koga K, Masuda S, et al.
Pages: 1443 - 1469
Abstract: AbstractAn impulsive solar flare was observed on 2012 June 3 by the Geostationary Operational Environment Satellite. In this flare, a salient feature was recognized whereby high-energy ions were accelerated to a few GeV within one minute. Associated with this flare, high-energy gamma-rays as well as high-energy neutrons were detected by the Space Environment Data Acquisition equipment onboard the International Space Station. A remarkable feature found of this event was an exceedingly high n$/$γ-ratio observed between the intensities of high-energy neutrons and gamma-rays. To understand a high n$/$γ-ratio of about 600, the interaction processes between the accelerated ions and ambient solar atmosphere were simulated for various test cases, taking into account the magnetic field of the photosphere. The simulation was extended by using the GEANT4 code and it was shown that the observed results could be reproduced under certain conditions selected for the actual interaction process. The results suggest that helium and C, N, and O ions were predominantly accelerated in this flare, and that high-energy gamma-rays and neutrons were produced by interactions between the accelerated ions and the ambient gas. As a result, a high n$/$γ-ratio was produced.
PubDate: Tue, 12 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab089
Issue No: Vol. 73, No. 6 (2021)
- BM UMa: A middle shallow contact binary at pre-transition stage of
evolution from W-type to A-type
Authors: Sarotsakulchai T; Soonthornthum B, Poshyachinda S, et al.
Pages: 1470 - 1485
Abstract: AbstractIn this study, all unpublished time series photometric data of BM UMa (q ∼ 2.0, P = 0.2712 d) from available archives were re-investigated together with new data taken from the 2.4-m Thai National Telescope of the Thai National Observatory. Based on period analysis, there is a short-term variation superimposed on the long-term period decrease. The trend of period change can be fitted with a downward parabolic curve indicating a period decrease at a rate of dP/dt = −3.36(±0.02) × 10−8 d yr−1. This long-term period decrease can be explained by mass transfer from the more massive component (M2 ∼ 0.79M⊙) to the less-massive one (M1 ∼ 0.39M⊙), in combination with angular momentum loss. For photometric study, we found that the binary consists of K0 V stars and at the intermediate shallow of contact configuration with evolution of fill-out factor from 8.8% (in 2007) to 23.2% (in 2020). Those results suggest that the binary is at the pre-transition stage of evolution from W-type to A-type, agreeing with the results of statistical study of W-type contact binaries. The mass of M2 will be decreased close to or below M1 and the mass ratio will be decreased (q < 1.0). In this way, the binary will evolve into an A-type as a deeper normal over-contact system with period increase. Finally, the binary will become a merger or a rapid-rotating single star when the mass ratio meets the critical value (q < 0.094), and produce a red nova.
PubDate: Tue, 12 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab090
Issue No: Vol. 73, No. 6 (2021)
- Fundamental parameters for 30 faint open clusters with Gaia EDR3 based on
the more reliable members
Authors: Ding X; Ji K, Li X, et al.
Pages: 1486 - 1496
Abstract: AbstractAn open cluster is an ideal region to study the evolution of stars. In this work, we use Gaia Early Data Release 3 (Gaia EDR3) to derive the fundamental parameters of 30 faint open clusters listed in the catalogue given by Cantat-Gaudin et al. (2018, A&A, 618, A93), but the G magnitude of all of the member stars of that catalogue is brighter than ∼18 mag. This catalogue does not provide isochrone fitting parameters and spatial structure parameters. We acquired the member stars of 30 open clusters using the Density-Based Spatial Clustering of Applications with Noise algorithm in Gaia EDR3. The G magnitude of the member stars using our method can be found down to ∼21 mag. The G-band, GBP-band, and GRP-band data of the member stars construct a good color–magnitude diagram, which can further ensure the precision of isochrone fitting. We also calculated the spatial structure parameters, which are the core radius and the limiting radius, using Markov chain Monte Carlo algorithm.
PubDate: Wed, 29 Sep 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab091
Issue No: Vol. 73, No. 6 (2021)
- Dragged surfaces. On the accretion tori in the ergoregion
Authors: Pugliese D; Stuchlík Z.
Pages: 1497 - 1539
Abstract: AbstractWe discuss the conditions for the existence of extended matter configurations orbiting in the ergoregion or close to the outer ergosurface of the Kerr black hole (“dragged” configurations). The co-rotating tori under consideration are perfect fluid configurations with barotropic equations of state, orbiting on the equatorial plane of the central Kerr black hole. The possibility of magnetized tori with a toroidal magnetic field is also discussed. Indications on the attractors where dragged tori can be observed are provided with the analysis of the fluid characteristics and geometrical features, relevant for the torus stability and their observations. QPO emissions from the inner edges of the dragged tori are also discussed. We argue that the smaller dragged tori could be subjected to a characteristic instability: the effect of the frame-dragging. This possibility is thoroughly explored. This can finally lead to the destruction of the torus (disk exfoliation) which can combine with accretion and processes present in the region very close to the black hole horizon. Tori are characterized according to the central attractor dimensionless spin. These structures can be observed in orbiting black holes with dimensionless spin a > 0.9897 M.
PubDate: Thu, 28 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab093
Issue No: Vol. 73, No. 6 (2021)
- Clump-scale chemistry in the NGC 2264-D cluster-forming region
Authors: Taniguchi K; Plunkett A, Shimoikura T, et al.
Pages: 1540 - 1555
Abstract: AbstractWe have conducted mapping observations toward the n3 and n5 positions in the NGC 2264-D cluster-forming region with the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 3. Observations with a 10000 au scale beam reveal the chemical composition at the clump scale. The spatial distributions of the observed low upper-state-energy lines of CH3OH are similar to those of CS and SO, and the HC3N emission seems to be predominantly associated with clumps containing young stellar objects. The turbulent gas induced by the star formation activities produces large-scale shock regions in NGC 2264-D, which are traced by the CH3OH, CS, and SO emissions. We derive the HC3N, CH3CN, and CH3CHO abundances with respect to CH3OH. Compared to the n5 field, the n3 field is farther (in projected apparent distance) from the neighboring NGC 2264-C, yet the chemical composition in the n3 field tends to be similar to that of the protostellar candidate CMM3 in NGC 2264-C. The HC3N$/$CH3OH ratios in the n3 field are higher than those in the n5 field. We find an anti-correlation between the HC3N$/$CH3OH ratio and their excitation temperatures. The low HC3N$/$CH3OH abundance ratio at the n5 field implies that the n5 field is an environment with more active star formation compared with the n3 field.
PubDate: Wed, 13 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab092
Issue No: Vol. 73, No. 6 (2021)
- A kinetics of the spinning gravitational field
Authors: Yamamoto T.
Pages: 1556 - 1562
Abstract: AbstractAccording to the general theory of relativity, a spinning shell drags its gravitational field. Owing to this frame-dragging effect, the gravitational field rotates. The spinning field also drags particles in the field. Although this moment of force is negligibly small, its kinetics should be properly handled. In this study, we show that the spinning gravitational field generates a central force, which makes the spinning shells heavy. The observed galactic rotation is naturally described by this central force without dark matter. We describe the kinetics of the spinning field and central force.
PubDate: Fri, 29 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab094
Issue No: Vol. 73, No. 6 (2021)
- Multi-frequency radio observations of the radio-loud magnetar XTE
J1810−197
Authors: Eie S; Terasawa T, Akahori T, et al.
Pages: 1563 - 1574
Abstract: AbstractWe report on the multi-frequency multi-epoch radio observations of the magnetar XTE J1810−197, which exhibited a radio outburst from 2018 December after its 10-year quiescent period. We performed quasi-simultaneous observations with VERA (22 GHz), Hitachi (6.9 GHz and 8.4 GHz), Kashima (2.3 GHz), and Iitate (0.3 GHz) radio telescopes located in Japan to trace the variability of the magnetar radio pulsations during the observing period from 2018 December 13 to 2019 June 12. The pulse width becomes narrower as the observing frequency goes higher, analogous to the general profile narrowing behavior of ordinary pulsars. When assuming a simple power law in the range of 2.3 GHz and 8.7 GHz, the radio spectrum of the magnetar goes steeper with the average spectral index 〈α〉 ≈ −0.85 for the first four months. The wide-band radio spectra gathered from our observations and the literature suggest that XTE J1810−197 would have a double-peaked spectrum with a valley point in 22–150 GHz, where the first spectral peak implies a gigahertz-peaked spectrum (GPS) feature with a peak at a few GHz. The GPS and the high-frequency peak have been identified in the spectra of other radio-loud magnetars, thus they may be intrinsic features that can give a new insight to the understanding of various emission mechanisms and the surrounding environments of radio magnetars. Our study emphasizes the importance of simultaneous long-term broad-band observations toward radio-loud magnetars to capture the puzzling spectral features and establish a link to other types of neutron stars.
PubDate: Tue, 02 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab098
Issue No: Vol. 73, No. 6 (2021)
- Subaru Hyper Suprime-Cam revisits the large-scale environmental dependence
on galaxy morphology over 360 deg2 at z = 0.3–0.6
Authors: Shimakawa R; Tanaka T, Toshikage S, et al.
Pages: 1575 - 1588
Abstract: AbstractThis study investigates the role of large-scale environments on the fraction of spiral galaxies at z = 0.3–0.6 sliced to three redshift bins of Δz = 0.1. Here, we sample 276220 massive galaxies in a limited stellar mass of 5 × 1010 solar mass (∼M*) over 360 deg2, as obtained from the Second Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). By combining projected two-dimensional density information (Shimakawa et al. 2021, MNRAS, 503, 3896) and the CAMIRA cluster catalog (Oguri et al. 2018, PASJ, 70, S20), we investigate the spiral fraction across large-scale overdensities and in the vicinity of red sequence clusters. We adopt transfer learning to reduce the cost of labeling spiral galaxies significantly and then perform stacking analysis across the entire field to overcome the limitations of sample size. Here we employ a morphological classification catalog by the Galaxy Zoo Hubble (Willett et al., 2017, MNRAS, 464, 4176) to train the deep learning model. Based on 74103 sources classified as spirals, we find moderate morphology–density relations on a 10 comoving Mpc scale, thanks to the wide-field coverage of HSC-SSP. Clear deficits of spiral galaxies have also been confirmed, in and around 1136 red sequence clusters. Furthermore, we verify whether there is a large-scale environmental dependence on rest-frame u − r colors of spiral galaxies; such a tendency was not observed in our sample.
PubDate: Wed, 20 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab097
Issue No: Vol. 73, No. 6 (2021)
- Dust dissipation timescales in the intermediate and outer regions of
protoplanetary disks
Authors: Maeshima H; Nakagawa T, Kojima T, et al.
Pages: 1589 - 1603
Abstract: AbstractDust and gas in protoplanetary disks dissipate as central stars evolve. In order to estimate the dust dissipation timescales in the protoplanetary disks, we stacked the WISE 12 and 22, and the AKARI 90 μm survey images of known T Tauri stars and derived the average fluxes, well below the survey flux limit in the 90 μm band. We classified 4783 T Tauri stars into three age groups, which are young (<2 Myr), mid-age (2–6 Myr), and old (>6 Myr) groups, and stacked the WISE 12 and 22 and the AKARI 90 μm images in each group. The photometry of the stacked image shows the flux decay timescales of 1.4 ± 0.2, 1.38 ± 0.05, and $1.4^{+0.6}_{-0.5}\:$Myr in the 12, 22, and 90 μm bands, respectively. In optically thin disks with one-solar luminosity central stars, the 12 and 22 μm fluxes are attributed to the emission from the intermediate (∼1 au) region and the 90 μm flux corresponds to that from the outer (∼10 au) region in the disk. We hence conclude that the dust dissipation timescale is τmed,dust ∼ 1.4 Myr in the intermediate disks and is $\tau _{\rm outer,dust}= 1.4^{+0.6}_{-0.5}\:$Myr in the outer disks. The dust-dissipation time difference between the outer and intermediate disks is $\Delta \tau _{\rm dust} = \tau _{\rm outer,dust} -\tau _{\rm med,dust}=0.0^{+0.6}_{-0.5}\:$Myr, indicating that the dust in the intermediate and outer disks dissipates on almost the same timescale.
PubDate: Thu, 28 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab095
Issue No: Vol. 73, No. 6 (2021)
- Reddening and darkening trends of on/off swirls and the relationship with
magnetic field strength
Authors: Cho E; Sim C, Baek S, et al.
Pages: 1604 - 1614
Abstract: AbstractLunar swirls are albedo features associated with magnetic anomalies, and their formation mechanism has long been debated. Because spectral properties of lunar swirls provide information on space weathering environments and surface compositions, differences in the spectra between swirls and background regions can give a clue to their formation. We analyze space weathering for swirls in the lunar highlands and maria using the VIS-NIR spectral slope, 1550 nm reflectance, and 950 nm band depth. We find that highland swirls show lower reddening-to-darkening ratios than off-swirl regions, implying more decreases of nanophase iron relative to microphase iron on swirls. We also use magnetic field data to investigate the influence of the crustal magnetic field on the space weathering of a few selected swirls. The Reiner Gamma swirl becomes more immature as the magnetic field strength increases, although the entire swirl has a high albedo. Especially, the Reiner Gamma tail shows that the stronger magnetic field makes the surface undergo less spectral reddening. Our results support the solar wind stand-off hypothesis, which is that the solar wind deflected by the crustal field determines the optical property of the surface.
PubDate: Wed, 20 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab096
Issue No: Vol. 73, No. 6 (2021)
- Precision of measurements and the biases due to the geomagnetic
declination in the Korean observations of the comet C/1723 T1
Authors: Ahn S.
Pages: 1615 - 1630
Abstract: AbstractPositions of the comet C/1723 T1 recorded in Korean historical resources are analysed to estimate the precision of measurements and the bias due to the geomagnetic declination at Seoul. We calculate the ephemeris of the comet by adopting the orbital elements determined by Gustav Spörer in 1843 based upon the Bradley’s telescopic observations in 1723. We confirm that the Bradley’s observations have a measurement error of 25″. The positions of the comet recorded in the Korean manuscripts are compared with the modern ephemeris. We find that there are misalignments in the instrument’s polar axis with Earth’s rotation axis: if the measurements were rounded up, there are alignment errors of 0.°0 ± 0.°2 in elevation and $-{0{_{.}^{\circ}}3}\pm {0{_{.}^{\circ}}3}$ in azimuth (to 1σ); if the measurements were rounded down, there are alignment errors of −0.°5 ± 0.°4 in elevation and +0.°5 ± 0.°6 in azimuth (to 1σ). Assuming that the instrument’s polar axis was aligned with a magnetic compass, we can regard the misalignment of the polar axis in azimuth as the geomagnetic declination at Seoul in 1723. We find that the geomagnetic declination obtained is in agreement with the recent models of the historical geomagnetic fields. We also obtain the one-time measurement error of ${0{_{.}^{\circ}}25}$, which is not different from the one-time measurement error of ${0{_{.}^{\circ}}3}$ obtained from the observational data of Mars in 1491.
PubDate: Fri, 29 Oct 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab099
Issue No: Vol. 73, No. 6 (2021)
- Subaru/FOCAS IFU revealed the metallicity gradient of a local extremely
metal-poor galaxy
Authors: Kashiwagi Y; Inoue A, Isobe Y, et al.
Pages: 1631 - 1637
Abstract: AbstractWe present the first measurement of the metallicity gradient in extremely metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph (FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG, HSC J1631+4426, whose oxygen abundance and stellar mass are known to be 12 + log (O/H) = 6.9 and log10(M*/M⊙) = 5.8, respectively. The measured metallicity gradient is −0.36 ± 0.04 dex kpc−1 corresponding to −0.049 ± 0.006 dex$\:R_\mathrm{e}^{-1}$ for the continuum effective radius of Re = 0.14 kpc. Our observation has successfully demonstrated that three-dimensional spectroscopy with 8 m-class telescopes is powerful enough to reveal the metallicity distribution in local EMPGs, providing precious information on the baryon cycle in local analogs of primordial galaxies in the early Universe.
PubDate: Tue, 02 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab100
Issue No: Vol. 73, No. 6 (2021)
- High-spatial resolution long-mid-infrared observations of massive
star-forming regions: Local star formation sequence
Authors: Uchiyama M; Miyata T, Sako S, et al.
Pages: 1638 - 1655
Abstract: AbstractThe formation of massive stars in dense and cold molecular clouds is a fundamental problem in star formation. In this work, we studied three compact massive star-forming regions, M8E, RAFGL 6366S, and IRAS 18317−0513, to investigate the environment of massive star formation, specifically the possibility of a local feedback process. Our new mid-infrared observations using miniTAO/MAX38 at 31 and 37 μm resolved individual objects in each region and allowed us to obtain their individual luminosities and masses. Together with existence/absence of ultra-compact H ii regions, it is suggested that less-massive objects are more evolved than the more-massive objects in two out of the three regions. Because the objects that are more massive evolve faster, those that are less massive form earlier. This formation trend of local mass-sequential star was first suggested in 0.1 pc-scale massive star-forming regions. Therefore, feedback, such as outflows, jets, or radiative heating, from previously formed lower-mass young stellar objects might affect the environment of parental clouds and lead to next-generation massive young stellar objects.
PubDate: Tue, 02 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab101
Issue No: Vol. 73, No. 6 (2021)
- Disentangling the stellar inclination of transiting planetary systems:
Fully analytic approach to the Rossiter–McLaughlin effect incorporating
the stellar differential rotation
Authors: Sasaki S; Suto Y.
Pages: 1656 - 1668
Abstract: AbstractThe Rossiter–McLaughlin (RM) effect has been widely used to estimate the sky-projected spin-orbit angle, λ, of transiting planetary systems. Most of the previous analysis assumes that the host stars are rigid rotators in which the amplitude of the RM velocity anomaly is proportional to v⋆ sin i⋆. When their latitudinal differential rotation is taken into account, one can break the degeneracy, and determine separately the equatorial rotation velocity v⋆ and the inclination i⋆ of the host star. We derive a fully analytic approximate formula for the RM effect adopting a parametrized model for the stellar differential rotation. For those stars that exhibit a differential rotation similar to that of the Sun, the corresponding RM velocity modulation amounts to several m s−1. We conclude that the latitudinal differential rotation offers a method to estimate i⋆, and thus the full spin-orbit angle ψ, from the RM data analysis alone.
PubDate: Mon, 08 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab102
Issue No: Vol. 73, No. 6 (2021)
- Proper motions of water masers in the star-forming region IRAS
23139+5939†‡
Authors: Trinidad M; Imai H, de la Fuente E, et al.
Pages: 1669 - 1680
Abstract: AbstractWe observed H2O (616→523) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA, a combination of very long baseline interferometry (VLBI) arrays between the Korean VLBI Network and the VLBI Exploration of Radio Astrometry (Japan). Through multi-epoch KaVA observations, we detected three groups of maser features, two of which coincide with those previously detected by the Karl G. Jansky Very Large Array. By determining the maser proper motions, we found that the first of maser groups exhibits an expanding motion that traces a wide-angle outflow almost along the line of sight, while the second one seems to be associated with the envelope of an H ii region. We discuss the star formation activity in IRAS 23139+5939, which may be reflected in the high variability of H2O masers associated with an outflow seen from the front.
PubDate: Wed, 03 Nov 2021 00:00:00 GMT
DOI: 10.1093/pasj/psab103
Issue No: Vol. 73, No. 6 (2021)
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