Search

We present our follow-up observations to search for an electromagnetic counterpart of the IceCube high-energy neutrino, IceCube-170922A. Monitoring observations of a likely counterpart, TXS 0506+056, are also described. First, we quickly took optical and near-infrared images of 7 flat-spectrum radio sources within the IceCube error region right after the neutrino detection and found a rapid flux decline of TXS 0506+056 in Kanata/HONIR J-band data. Motivated by this discovery, intensive follow-up observations of TXS 0506+056 are continuously done, including our monitoring imaging observations, spectroscopic observations, and polarimetric observations in optical and near-infrared wavelengths. TXS 0506+056 shows a large amplitude (~1.0 mag) variability in a time scale of several days or longer, although no significant variability is detected in a time scale of a day or shorter. TXS 0506+056 also shows a bluer-when-brighter trend in optical and near-infrared wavelengths. Structure functions of variabilities are examined and indicate that TXS 0506+056 is not a special blazar in terms of optical variability. Polarization measurement results of TXS 0506+056 are also discussed., 19 pages, 10 figures, 4 tables. Accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

Flares are thought to be the rapid releases of magnetic energy through magnetic reconnection in the corona. Blue asymmetries (enhancement of the blue wing) in chromospheric lines have been widely observed during flares on M dwarfs. They are thought to be caused by the upward motions of cool plasma (e.g., chromospheric evaporations, filament/prominence eruptions). As observed on the Sun, stellar filament/prominence eruptions can evolve into stellar CMEs (coronal mass ejections). Here we report the results from spectroscopic and photometric observations of the M-type flare star YZ CMi in the framework of the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) collaborations during the Transiting Exoplanet Survey Satellite (TESS) observation period. We detected 145 white-light flares from the TESS light curve and 4 H\(\alpha\) flares from the OISTER observations performed between 2019-01-16 and 2019-01-18. Among them, 3 H\(\alpha\) flares were associated with white-light flares. However, one of them did not show clear brightening in continuum; during this flare, the H\(\alpha\) line exhibited blue-asymmetry which has lasted for \(\sim 60\) min. The line of sight velocity of the blue-shifted component is \(-80\) - \(-100\) km s-1. By assuming that the blue-asymmetry in H\(\alpha\) line was caused by a prominence eruption on YZ CMi, we estimated the mass and kinetic energy of the upward-moving material to be \(10^{16}\) - \(10^{18}\) g and \(10^{29.5}\) - \(10^{31.5}\) erg, respectively. Although, the estimated mass is comparable to expectations from the empirical relation between the flare X-ray energy and mass of upward-moving material for solar CMEs, the estimated kinetic energy for the non-white-light flare on YZ CMi is roughly 2 orders of magnitude smaller than that expected from the relation between flare X-ray energy and kinetic energy for solar CMEs. This could be understood by the difference in the velocity between CMEs and prominence eruptions., {"references":["Airapetian, V. S., et al. (2020), Int. J. Astrobiology, 19, 136. doi:10.1017/S1473550419000132","Argiroffi C., et al. (2019), Nature Astron., 3, 742. doi:10.1038/s41550-019-0781-4","Gopalswamy N., et al., (2003), ApJ, 586, 562. doi:10.1086/367614","Honda S., et al. (2018), PASJ, 70, 62. doi:10.1093/pasj/psy055","Moschou S.-P., et al. (2019), ApJ, 877, 105. doi:10.3847/1538-4357/ab1b37","Shibata, K., et al. (1995), ApJ Lett., 451, L83. doi:10.1086/309688","Vida, K., et al. (2016), A&A, 590, A11. doi:10.1051/0004-6361/201527925","Vida, K., et al. (2019), A&A, 623, A49. doi:10.1051/0004-6361/201834264","Yamashiki, Y. A., et al. (2019), ApJ, 881, 114. doi:10.3847/1538-4357/ab2a71","Yashiro S., Gopalswamy N. (2009), in IAU Symp. 257, Universal Heliophysical Processes, ed. Gopalswamy N., Webb D. F. (Cambridge: Cambridge University Press), 233. doi:10.1017/S1743921309029342"]}

We report multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with Seimei Telescope (6150--7930 {\AA}), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700--7500 {\AA}), NICER (Neutron Star Interior Composition Explorer; 0.2--12.0 keV), and collaborations of OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total which include ten H$\alpha$, four X-ray, and four optical-continuum flares; one of them is a superflare with the total energy of $\sim$ 2.0$\times$10$^{33}$ erg. We found that (1) during the superflare, the H$\alpha$ emission line full width at 1/8 maximum dramatically increases to 14 {\AA} from 8 {\AA} in the low-resolution spectra (R$\sim$ 2000) accompanied with the large white-light flares, (2) some weak H$\alpha$/X-ray flares are not accompanied with white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and H$\alpha$ intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed by using the RADYN code. As a result of simulations, we found the simulated H$\alpha$ line profiles with hard and high-energy non-thermal electron beams are consistent with that of the initial phase line profiles of the superflares, while those with more soft- and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we found that the relation between optical continuum and H$\alpha$ intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares., Comment: 18 pages, 17 figures, Accepted for Publication in PASJ

An extensive spectroscopic study on \xi Boo A (chromospherically active solar-type star) was conducted based on the spectra obtained in 2008 December though 2010 May, with an aim to detect any spectrum variability and to understand its physical origin. For each spectrum, the atmospheric parameters were spectroscopically determined based on Fe lines, and the equivalent widths (along with the line-broadening parameters) of selected 99 lines were measured. We could detect meaningful small fluctuations in the equivalent widths of medium-strength lines. This variation was found to correlate with the effective temperature (T_eff) consistently with the T-sensitivity of each line, which indicates that the difference in the mean temperature averaged over the disk of inhomogeneous condition is mainly responsible for this variability. It was also found that the macrobroadening widths of medium-strength lines and the equivalent widths dispersion of saturated lines tend to increase with the effective Lande factor, suggesting an influence of magnetic field. Our power spectrum analysis applied to the time-sequence data of V I/Fe II line-strength ratio and T_eff could not confirm the 6.4 d period reported by previous studies. We suspect that surface inhomogeneities of \xi Boo A at the time of our observations were not so much simple (such as single star patch) as rather complex (e.g., intricate aggregate of spots and faculae)., Comment: 22 pages with online material, accepted for publication in Publ. Astron. Soc. Japan (2020)

Star spot evolution is visible evidence of the emergence/decay of the magnetic field on stellar surface, and it is therefore important for the understanding of the underlying stellar dynamo and consequential stellar flares. In this paper, we report the temporal evolution of individual star spot area on the hot-Jupiter-hosting active solar-type star Kepler 17 whose transits occur every 1.5 days. The spot longitude and area evolution are estimated (1) from the stellar rotational modulations of Kepler data and (2) from the brightness enhancements during the exoplanet transits caused by existence of large star spots. As a result of the comparison, number of spots, spot locations, and the temporal evolution derived from the rotational modulations is largely different from those of in-transit spots. We confirm that although only two light curve minima appear per rotation, there are clearly many spots present on the star. We find that the observed differential intensity changes are sometimes consistent with the spot pattern detected by transits, but they sometimes do not match with each other. Although the temporal evolution derived from the rotational modulation differs from those of in-transit spots to a certain degree, the emergence/decay rates of in-transit spots are within an order of magnitude of those derived for sunspots as well as our previous research based only on rotational modulations. This supports a hypothesis that the emergence/decay of sunspots and extremely-large star spots on solar-type stars occur through the same underlying processes., Comment: 37 pages, 12 figures, 1 table. Accepted for publication in The Astrophysical Journal

It has been occasionally suggested that Fe abundances of K dwarfs derived from Fe I and Fe II lines show considerable discrepancies and oxygen abundances determined from high-excitation O I 7771-5 triplet lines are appreciably overestimated (the problem becoming more serious towards lower Teff), which however has not yet been widely confirmed. With an aim to clarify this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe I/Fe II ionization equilibrium as usual, and determined their oxygen abundances by applying the non-LTE spectrum fitting analysis to O I 7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and log g from the well-determined solutions of Hyades dwarfs are mostly ~4500K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale., Comment: Accepted for publication in Astronomical Journal, 38 pages (including 14 figures and 2 tables), with supplementary online material

Recently, many superflares on solar-type stars were discovered as white-light flares (WLFs). A correlation between the energies (E) and durations (t) of superflares is derived as $t\propto E^{0.39}$, and this can be theoretically explained by magnetic reconnection ($t\propto E^{1/3}$). In this study, we carried out a statistical research on 50 solar WLFs with SDO/HMI to examine the t-E relation. As a result, the t-E relation on solar WLFs ($t\propto E^{0.38}$) is quite similar stellar superflares, but the durations of stellar superflares are much shorter than those extrapolated from solar WLFs. We present the following two interpretations; (1) in solar flares, the cooling timescale of WL emission may be longer than the reconnection one, and the decay time can be determined by the cooling timescale; (2) the distribution can be understood by applying a scaling law $t\propto E^{1/3}B^{-5/3}$ derived from the magnetic reconnection theory., 4 pages, 1 figures, paper of the Proceedings of the IAUS340, accepted

Small stellar systems like dwarf galaxies are suggested to be the main building blocks of our Galaxy by numerical simulations in Lambda CDM models. The existence of star streams like Sagittarius tidal stream indicates that dwarf galaxies play a role in the formation of the Milky Way. However, it is unclear how many and what kind of stars in our Galaxy are originated from satellite dwarf galaxies, which could be constrained by chemical abundances of metal-poor stars. Here we report on the discovery of a metal-poor star with an extreme r-process enhancement and alpha-element deficiency. In this star, the abundance ratio of the r-process element Eu with respect to Fe is more than one order of magnitude higher than the Sun and the metallicity is 1/20 of the solar one. Such kind of stars have been found in present-day dwarf galaxies, providing the clearest chemical signature of past accretion events. The long timescale of chemical evolution of the host dwarf galaxy expected from the abundance of alpha element with respect to Fe suggests that the accretion occurred in a relatively late phase compared to most of the accretions that formed the bulk of the Milky Way halo., Comment: Accepted for publication in Nature Astronomy

We report the latest statistical analyses of superflares on solar-type (G-type main-sequence; effective temperature is 5100 - 6000 K) stars using all of the $Kepler$ primary mission data, and $Gaia$-DR2 (Data Release 2) catalog. We updated the flare detection method from our previous studies by using high-pass filter to remove rotational variations caused by starspots. We also examined the sample biases on the frequency of superflares, taking into account gyrochronology and flare detection completeness. The sample size of solar-type stars and Sun-like stars (effective temperature is 5600 - 6000 K and rotation period is over 20 days in solar-type stars) are $\sim$4 and $\sim$12 times, respectively, compared with Notsu et al. (2019, ApJ, 876, 58). As a result, we found 2341 superflares on 265 solar-type stars, and 26 superflares on 15 Sun-like stars: the former increased from 527 to 2341 and the latter from 3 to 26 events compared with our previous study. This enabled us to have a more well-established view on the statistical properties of superflares. The observed upper limit of the flare energy decreases as the rotation period increases in solar-type stars. The frequency of superflares decreases as the stellar rotation period increases. The maximum energy we found on Sun-like stars is $4 \times 10^{34}$ erg. Our analysis of Sun-like stars suggest that the Sun can cause superflares with energies of $\sim 7 \times 10^{33}$ erg ($\sim$X700-class flares) and $\sim 1 \times 10^{34}$ erg ($\sim$X1000-class flares) once every $\sim$3,000 years and $\sim$6,000 years, respectively., 49 pages, 22 figures, 6 tables, supplementary table, Accepted for publication in The Astrophysical Journal (03-Nov-2020)

We present the results of the high-resolution spectroscopy of the FU Orionis-type star V960 Mon. The brightness of V960 Mon decreased continuously after the outburst was detected in 2014 November. During this dimming event, we have carried out medium-resolution spectroscopic monitoring observations and found that the equivalent width of the absorption features showed variations. To further investigate the spectroscopic variations, we conducted a high-resolution spectroscopic observation of V960 Mon with the Subaru Telescope and the High Dispersion Spectrograph on 2018 January 8 and 2020 February 1. By comparing this spectrum with the archival data of the Keck Observatory and the High Resolution Echelle Spectrometer taken between 2014 and 2017, we found that the absorption profiles changed as V960 Mon faded. The line profile of absorption lines such as Fe I and Ca I can be explained by a sum of the spectra of the disk atmosphere and the central star. The model spectrum created to explain the variations of the line profiles suggests that the effective temperature of the central star is $\sim$5500 K, which is comparable to that of the pre-outburst phase with a distance of 1.6 kpc with Gaia. The spectrum also shows that the effective temperature of the disk atmosphere decreased as V960 Mon faded. The variations of the H$\alpha$ and Ca II lines (8498.0 A, 8542.1 A) also show that the V960 Mon spectrum became central-star dominant., Comment: 16 pages, 11 figures, accepted for publication in ApJ

There are several peculiar long-period dwarf-nova like objects, which show rare, low-amplitude outbursts with highly ionized emission lines. 1SWASP J162117$+$441254, BD Pav, and V364 Lib belong to this kind of objects. Some researchers even doubt whether 1SWASP J1621 and V364 Lib have the same nature as normal dwarf novae. We studied the peculiar outbursts in these three objects via our optical photometry and spectroscopy, and performed numerical modeling of their orbital variations to investigate their properties. We found that their outbursts lasted for a long interval (a few tens of days), and that slow rises in brightness were commonly observed during the early stage of their outbursts. Our analyses and numerical modeling suggest that 1SWASP J1621 has a very high inclination, close to 90 deg, plus a faint hot spot. Although BD Pav seems to have a slightly lower inclination ($\sim$75 deg), the other properties are similar to those in 1SWASP J1621. On the other hand, V364 Lib appears to have a massive white dwarf, a hot companion star, and a low inclination ($\sim$35 deg). In addition, these three objects possibly have low transfer rate and/or large disks originating from the long orbital periods. We find that these properties of the three objects can explain their infrequent and low-amplitude outbursts within the context of the disk instability model in normal dwarf novae without strong magnetic field. In addition, we suggest that the highly-ionized emission lines in outburst are observed due to a high inclination and/or a massive white dwarf. More instances of this class of object may be unrecognized, since their unremarkable outbursts can be easily overlooked., Comment: 17 pages, 18 figures, 2 tables with supporting information. Accepted for publication in PASJ

Capella is a spectroscopic binary consisting of two G-type giants, where the primary (G8III) is a normal red-clump giant while the secondary (G0III) is a chromospherically-active fast rotator showing considerable overabundance of Li as Li-enhanced giants. Recently, Takeda & Tajitsu (2017) reported that abundance ratios of specific light elements (e.g., [C/Fe] or [O/Fe]) in Li-rich giants of high activity tend to be anomalously high, which they suspected to be nothing but superficial caused by unusual atmospheric structure due to high activity. Towards verifying this hypothesis, we determined the elemental abundances of the primary and the secondary of Capella based on the disentangled spectrum of each component, in order to see whether any apparent disagreement exists between the two, which should have been formed with the same chemical composition. We found that the primary is slightly supersolar (by ~+0.1dex) while the secondary is subsolar (by several tenths dex) for heavier elements such as Fe, resulting in a marked discrepancy between the primary and secondary, though such a trend is not seen for light elements (e.g., C or O). These observational facts suggest that anomalously large [X/Fe] ratios found in Li-rich giants were mainly due to an apparent decrease of Fe abundance, which we speculate is caused by the overionization effect due to chromospheric UV radiation. We thus conclude that conventional model atmosphere analysis would fail to correctly determine the abundances of fast-rotating giants of high activity, for which proper treatment of chromospheric effect is required for deriving true photospheric abundances., 39 pages, 12 figures and 4 tables (with online material in "anc" directory), accepted for publication in Astrophysical Journal

We have performed 5 night spectroscopic observation of the Halpha line of EV Lac with a medium wavelength resolution (R~ 10,000) using the 2m Nayuta telescope at the Nishi-Harima Astronomical Observatory. EV Lac always possesses the Halpha emission line; however, its intensity was stronger on August 15, 2015 than during other four-night periods. On this night, we observed a rapid rise (~ 20min) and a subsequent slow decrease (~ 1.5h) of the emission-line intensity of Halpha, which was probably caused by a flare. We also found an asymmetrical change in the Halpha line on the same night. The enhancement has been observed in the blue wing of the Ha line during each phase of this flare (from the flare start to the flare end), and absorption components were present in its red wing during the early and later phases of the flare. Such blue enhancement (blue asymmetry) of the Halpha line is sometimes seen during solar flares, but only during the early phases. Even for solar flares, little is known about the origin of the blue asymmetry. Compared with solar-flare models, the presented results can lead to the understanding of the dynamics of stellar flares., 17 Pages, 9 figures, Accepted for Publication in PASJ

Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotations with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations on the emergence and decay processes of star spots, which are important to understand underlying stellar dynamo and stellar flares. In this study, we measured temporal evolutions of star spot area with Kepler data by tracing local minima of the light curves. In this analysis, we extracted temporal evolutions of star spots showing clear emergence and decay without being disturbed by stellar differential rotations. We applied this method to 5356 active solar-type stars observed by Kepler and obtained temporal evolutions of 56 individual star spots. We calculated lifetimes, emergence and decay rates of the star spots from the obtained temporal evolutions of spot area. As a result, we found that lifetimes ($T$) of star spots are ranging from 10 to 350 days when spot areas ($A$) are 0.1-2.3 percent of the solar hemisphere. We also compared them with sunspot lifetimes, and found that the lifetimes of star spots are much shorter than those extrapolated from an empirical relation of sunspots ($T\propto A$), while being consistent with other researches on star spot lifetimes. The emerging and decay rates of star spots are typically $5 \times 10^{20}$ $\rm Mx\cdot h^{-1}$ ($8$ $\rm MSH\cdot h^{-1}$) with the area of 0.1-2.3 percent of the solar hemisphere and are mostly consistent with those expected from sunspots, which may indicate the same underlying processes., Comment: 19 pages, 11 figures, accepted for publication in ApJ

We present the results of the spectroscopic monitoring of the FU Orionis type star V960 Mon. Spectroscopic variations of a FU Orionis type star will provide valuable information of its physical nature and the mechanism of the outburst. We conducted medium-resolution (R~10000) spectroscopic observations of V960 Mon with 2m Nayuta telescope at the Nishi-Harima Astronomical Observatory, from 2015 January to 2017 January for 53 nights in total. We focused on H alpha line and nearby atomic lines, and detected the strength variations in both absorption and emission lines. The observed variation in the equivalent width of the absorption lines correspond to a decrease in effective temperature and increase in surface gravity. These variations were likely to originate from the luminosity fading of the accretion disk due to the decrease in mass accretion rate., Comment: 10 pages, 5 figures, accepted for publication in AJ

We report progresses of a joint project on searching for extremely metal-poor (EMP) stars based on LAMOST survey and Subaru follow-up observation. Follow-up high-resolution snapshot spectra have been obtained for 70 objects, resulting in 42 EMP stars. A number of chemically interesting objects have already been identified, including (1) Two UMP (ultra metal-poor) stars with [Fe/H] ~ −4.0. One of them is the second UMP turnoff star with Li detection. (2) A super Li-rich (A(Li) ~ 3.1) EMP giant. This is the most metal-poor and extreme example of Li enhancement in giants known to date, and will shed light on Li production during the evolution of red giants. (3) A few EMP stars showing extreme overabundance in heavy elements. Detailed abundances of these extreme objects and statistics obtained by the large sample of EMP stars will provide important constraints on the Galactic halo formation.

We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits a large excess of r -process elements with [Eu/Fe] ~ +1.16. The star is one of the newly discovered EMP stars identified from the LAMOST low-resolution spectroscopic survey and a high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the “normal” population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r −II metal-poor giants such as CS 22892−052 and CS 31082−001. The abundances of elements in the range from Ba through Dy match the scaled solar r -process pattern well. LAMOST J110901.22+075441.8 provides the first detailed measurements of neutron-capture elements among r −II stars at such low metallicity with [Fe/H] ≾ −3.4, and exhibits similar behavior as other r −II stars in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu.

We analyze the correlation between starspots and superflares on solar-type stars using observations from the Kepler mission. The analysis shows that the observed fraction of stars with superflares decreases as the rotation period increases and as the amplitude of photometric variability associated with rotation decreases. We found that the fraction of stars with superflares among the stars showing large-amplitude rotational variations, which are thought to be the signature of the large starspots, also decreases as the rotation period increases. The small fraction of superflare stars among the stars with large starspots in the longer-period regime suggests that some of the stars with large starspots show a much lower flare activity than the superflare stars with the same spot area. Assuming simple relations between spot area and lifetime and between spot temperature and photospheric temperature, we compared the size distribution of large starspot groups on slowly-rotating solar-type stars with that of sunspot groups. The size distribution of starspots shows the power-law distribution and the size distribution of larger sunspots lies on this power-law line. We also found that frequency-energy distributions for flares originating from spots with different sizes are the same for solar-type stars with superflares and the Sun. These results suggest that the magnetic activity we observe on solar-type stars with superflares and that on the Sun is caused by the same physical processes., Accepted for publication in PASJ

We present the early-phase spectra and the light curves of the broad-lined supernova (SN) 2016coi from $t=7$ to $67$ days after the estimated explosion date. This SN was initially reported as a broad-lined Type SN Ic (SN Ic-BL). However, we found that spectra up to $t=12$ days exhibited the He~{\sc i} $\lambda$5876, $\lambda$6678, and $\lambda$7065 absorption lines. We show that the smoothed and blueshifted spectra of normal SNe Ib are remarkably similar to the observed spectrum of SN 2016coi. The line velocities of SN 2016coi were similar to those of SNe Ic-BL and significantly faster than those of SNe Ib. Analyses of the line velocity and light curve suggest that the kinetic energy and the total ejecta mass of SN 2016coi are similar to those of SNe Ic-BL. Together with broad-lined SNe 2009bb and 2012ap for which the detection of He~{\sc i} were also reported, these SNe could be transitional objects between SNe Ic-BL and SNe Ib, and be classified as broad-lined Type `Ib' SNe (SNe `Ib'-BL). Our work demonstrates the diversity of the outermost layer in broad-lined SNe, which should be related to the variety of the evolutionary paths., Comment: 9 pages, 10 figures. Accepted for publication in ApJ

High-resolution optical spectroscopy was conducted for the metal-poor post-AGB star CC Lyr to determine its chemical abundances and spectral line profiles. Our standard abundance analysis confirms its extremely low metallicity ([Fe/H], Comment: 17 pages, 5 figures, 5 tables, to appear Publication of Astronomical Society of Japan

The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the $z-H$ color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized $r$-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that $r$-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 $\Msun$, which suggests a more intense mass ejection ($\sim 0.03 \Msun$) or possibly an additional energy source., Comment: 7 pages, 5 figures. Published in PASJ (Publications of the Astronomical Society of Japan)

We present a summary of the splinter session "Sun-like stars unlike the Sun" that was held on 09 June 2016 as part of the Cool Stars 19 conference (Uppsala, Sweden). We discussed the main limitations (in the theory and observations) in the derivation of very precise stellar parameters and chemical abundances of Sun-like stars. We outlined and discussed the most important and most debated processes that can produce chemical peculiarities in solar-type stars. Finally, in an open discussion between all the participants we tried to identify new pathways and prospects towards future solutions of the currently open questions., Comment: Resubmitted to AN after minor revision

How huge early stars enriched the universe How big did the first generation of stars get? Knowing their size is critical to understanding how they enriched the chemistry of the universe through supernova explosions. According to numerical simulations, some of the earliest stars were more than 100 times the Sun's mass. However, no traces of these live-fast, die-young stars had been detected in any low-mass stars still extant from that era. Aoki et al. now show spectra of one such metal-poor star that may have recorded the activity of a very massive predecessor (see the Perspective by Bromm). This observational evidence will spur further supernova models, as none predicts this specific chemical signature. Science , this issue p. 912 ; see also p. 868

Multiple outbursts of a Jupiter-family comet, 15P/Finlay, occurred from late 2014 to early 2015. We conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 January 15.6-15.7. The gas, consisting mostly of C2 and CN, and dust particles expanded at speeds of 1,110 +/- 180 m/s and 570 +/- 40 m/s at a heliocentric distance of 1.0 AU. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity beta_max = 1.6 +/- 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 10^8-10^9 kg of dust particles (assumed to be 0.3 micron - 1 mm) were ejected through each outburst. Although the total mass is three orders of magnitude smaller than that of the 17P/Holmes event observed in 2007, the kinetic energy per unit mass (104 J/kg) is equivalent to the estimated values of 17P/Holmes and 332P/2010 V1 (Ikeya-Murakami), suggesting that the outbursts were caused by a similar physical mechanism. From a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15P/Finlay-class outbursts occur >1.5 times annually and inject dust particles from Jupiter-family comets and Encke-type comets into interplanetary space at a rate of ~10 kg/s or more., 37 pages, 9 figures

We present stellar parameters and abundances of 15 elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Y and Ba) for 23 field RR Lyrae variables based on high-resolution ( R ~ 60 000) and high signal-to-noise (S/N~ 200) spectra obtained using the High Dispersion Spectrograph on the Subaru Telescope. Six stars in the sample have more than one spectrum observed at different pulsation phases. The derived abundance ratios of [X/Fe] for 14 elements (except for Ba) do not vary during the pulsation cycle. An interesting curve of [Ba/Fe] versus phase is detected for the first time and it shows decreasing [Ba/Fe] with increasing temperature at a given metallicity. Combining with data in the literature, abundances of most RR Lyrae stars as a function of [Fe/H] follow the same trends as those of dwarf stars, but [Sc/Fe] and [Y/Fe] ratios of RR Lyrae stars at solar metallicity are lower than those of dwarf stars. The kinematics of RR Lyrae stars indicate that three comparatively metal-rich RR Lyrae stars might originate from the thick disk and they show higher [α/Fe] ratios than RR Lyrae stars with thin disk kinematics. Among 23 RR Lyrae stars, two special objects are found with abnormal abundances; TV Lib has high [α/Fe], [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios while TW Her has solar [α/Fe] but significantly lower [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios as compared with other RR Lyrae stars.

We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from $-11$ to $+140$ days after the date of its $B$-band maximum in the optical and near-infrared (NIR) wavelengths conducted through the OISTER ToO program. The NIR light curves and color evolutions up to 35 days after the $B$-band maximum provided an excellent match with those of another SC SN 2009dc, providing a further support to the nature of SN 2012dn as a SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from $30$ days after the $B$-band maximum. The $H$ and $K_{s}$-band light curves exhibited much later maximum dates at $40$ and $70$ days after the $B$-band maximum, respectively, compared with those of normal SNe Ia. The $H$ and $K_{s}$-band light curves subtracted by those of SN 2009dc displayed plateaued evolutions, indicating a NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to be $4.8 - 6.4\times10^{-2}$ pc. No emission lines were found in its early phase spectrum, suggesting that the ejecta-CSM interaction could not occur. On the other hand, we found no signature that strongly supports the scenario of dust formation. The mass loss rate of the pre-explosion system is estimated to be $10^{-6}-10^{-5}$ M$_{\odot}$ yr$^{-1}$, assuming that the wind velocity of the system is $10-100$ km~s$^{-1}$, which suggests that the progenitor of SN 2012dn could be a recurrent nova system. We conclude that the progenitor of this SC SN could be explained by the single-degenerate scenario., 22 pages, 10 pages, 8 tables, accepted for publication in PASJ. Reference corrected

Oxygen abundances of 34 B-type stars in the effective temperature range of Teff~10000-28000K with diversified rotational velocities (vesini~ 0-250km/s) were determined from the OI triplet lines at 7771-5A, with an aim to examine whether this OI feature can be a reliable abundance indicator for such high-temperature stars including rapid rotators. It revealed that the required non-LTE abundance correction is distinctly large (ranging from ~-0.6dex to ~-1.7dex) and its consideration is indispensable. On the condition that the non-LTE effect is taken into account, this triplet is a useful O abundance indicator (with a precision of ~200mA). In contrast, it is not adequate for abundance derivation for stars at Teff >~25000K, where its strength rapidly drops down toward a hardly detectable level (except for sharp-lined stars) and its sensitivity to Teff or log g becomes considerably large. The resulting non-LTE oxygen abundances turned out to be almost normal (i.e., near-solar around ~8.7-8.8 within +/-~0.2dex) for most stars without any dependence upon projected rotational velocity as well as luminosity (or mass), which is consistent with the prediction of recent stellar evolution calculations., Comment: 13 pages, 7 figures, 2 tables, and online material; accepted for publication in Publ. Astron. Soc. Japan

We searched for superflares on solar-type stars using the Kepler short-cadence (1-min sampling) data in order to detect superflares with short duration. We found 187 superflares on 23 solar-type stars whose bolometric energy ranges from the order of $10^{32}$ erg to $10^{36}$ erg. Using these new data combined with the results from the data with 30-min sampling, we found the occurrence frequency ($dN/dE$) of superflares as a function of flare energy ($E$) shows the power-law distribution ($dN/dE \propto E ^{-\alpha}$) with $\alpha=1.5$ for $10^{33}, Comment: 6 pages, 4 figures, submitted to the proceedings of the IAU Symposium 320 "Solar and Stellar Flares and Their Effects on Planets" (eds. A. G. Kosovichev, S. L. Hawley, P. Heinzel)

In order to investigate the carbon-to-oxygen ratio of the young open cluster M45 (Pleiades), the C and O abundances of selected 32 F-G type dwarfs (in the effective temperature range of Teff~5800-7600K and projected rotational velocity range of vesini~10-110km/s) belonging to this cluster were determined by applying the synthetic spectrum-fitting technique to C I 5380 and O I 6156-8 lines. The non-LTE corrections for these C I and O I lines were found to be practically negligible (less than a few hundredths dex). The resulting C and O abundances (along with the Fe abundance) turned out nearly uniform without any systematic dependence upon Teff or vesini. We found, however, in spite of almost solar Fe abundance ([Fe/H]~0), carbon turned out to be slightly subsolar ([C/H]~-0.1) while oxygen slightly supersolar ([O/H]~+0.1). This lead to a conclusion that [C/O] ratio was moderately subsolar (~-0.2) in the primordial gas from which these Pleiades stars were formed ~120--130 Myr ago. Interestingly, similarly young B-type stars are reported to show just the same result ([C/O]~-0.2), while rather aged (~1-10 Gyr) field F-G stars of near-solar metallicity yield almost the solar value ([C/O]~0) on the average. Such a difference in the C/O ratio between two star groups of distinctly different ages may be explained as a consequence of orbit migration mechanism which Galactic stars may undergo over a long time., Comment: 22 pages, 11 figures, 3 tables (+ 1 online data table) accepted for publication in Publ. Astron. Soc. Japan [Only the metadata has been updated (correction to a typo in the name of an author, insertion of the journal name) without any change to the manuscript.]

Recent studies of solar-type superflare stars have suggested that even old slowly rotating stars similar to the Sun can have large starspots and superflares. We conducted high dispersion spectroscopy of 49 nearby solar-analog stars (G-type main sequence stars with $T_{\rm{eff}}\approx5,600\sim6,000$ K) identified as ROSAT soft X-ray sources, which are not binary stars from the previous studies. We expected that these stars can be used as a proxy of bright solar-analog superflare stars, since superflare stars are expected to show strong X-ray luminosity. More than half (37) of the 49 target stars show no evidence of binarity, and their atmospheric parameters ($T_{\rm{eff}}$, $\log g$, and [Fe/H]) are within the range of ordinary solar-analog stars. We measured Ca II 8542 and H$\alpha$ lines, which are good indicators of the chromospheric activity. The intensity of these lines indicates that all the target stars have large starspots. We also measured $v\sin i$ (projected rotational velocity) and Lithium abundance for the target stars. Li abundance is a key to understanding the evolution of the stellar convection zone, which reflects the stellar age, mass and rotational history. We confirmed that many of the target stars rapidly rotate and have high Li abundance, compared with the Sun, as suggested by many previous studies. There are, however, also some target stars that rotate slowly ($v\sin i$=2$\sim$3 km s$^{-1}$) and have low Li abundance like the Sun. These results support that old and slowly rotating stars similar to the Sun could have high activity level and large starspots. This is consistent with the results of our previous studies of solar-type superflare stars. In the future, it is important to conduct long-term monitoring observations of these active solar-analog stars in order to investigate detailed properties of large starspots from the viewpoint of stellar dynamo theory., Comment: 52 pages, 18 figures, 6 tables, accepted for publication in PASJ. arXiv admin note: text overlap with arXiv:1412.8243

著者人数: 42名, Accepted: 2016-03-14, 資料番号: SA1160038000

Observations of superflares on solar-type stars indicate that they are associated with much larger starspots than appear on the Sun, occur more frequently on rapidly rotating stars and, contrary to a previous proposal, are not frequently associated with hot Jupiters. Solar flares are the most energetic explosions in the solar atmosphere, and similar flares occur on many stars. 'Superflares' many thousands of times more energetic than the average solar flare have been observed from a variety of stars, but the relatively small number observed on solar-type stars has hitherto precluded a detailed study of them. Now, on the basis of an analysis of data from the Kepler satellite, Maehara et al. report observations of 365 superflares, including 101 from slowly rotating solar-type stars, from a sample of around 83,000 stars observed over 120 days. The data suggest that superflares occur more frequently on rapidly rotating stars and on stars with 'starspots' much larger than the sunspots with which we are familiar. There is no historical record of superflares on the Sun in the past 2,000 years, and it is probable that none has occurred in the past one billion years. Bradley Schaefer discusses these findings in an accompanying News and Views, and concludes that it is extremely unlikely that the Sun will host a superflare. Solar flares are caused by the sudden release of magnetic energy stored near sunspots. They release 1029 to 1032 ergs of energy on a timescale of hours1. Similar flares have been observed on many stars, with larger ‘superflares’ seen on a variety of stars2,3, some of which are rapidly rotating4,5 and some of which are of ordinary solar type3,6. The small number of superflares observed on solar-type stars has hitherto precluded a detailed study of them. Here we report observations of 365 superflares, including some from slowly rotating solar-type stars, from about 83,000 stars observed over 120 days. Quasi-periodic brightness modulations observed in the solar-type stars suggest that they have much larger starspots than does the Sun. The maximum energy of the flare is not correlated with the stellar rotation period, but the data suggest that superflares occur more frequently on rapidly rotating stars. It has been proposed that hot Jupiters may be important in the generation of superflares on solar-type stars7, but none have been discovered around the stars that we have studied, indicating that hot Jupiters associated with superflares are rare.

We report the results of abundance analysis for high-resolution spectra of eight extremely metal-poor turn-off stars selected from SDSS/SEGUE. Based on differential analysis adopting stellar parameters from Balmer line profiles, we obtain the following results: i) Statistically significant scatter is found in [X/Fe] (X=Na, Mg, Cr, Ti, Sr and Ba), among which [Na/Fe] shows an apparent bimodal distribution, ii) Li abundances are ~0.3 dex lower in [Fe/H]

A detailed abundance analysis of the primary star of Aur before an eclipse was carried out using a very high signal-to-noise ratio optical-region spectrum. An A7 Iab supergiant HD 81471, presumably a member of the Vela OB1 association, was used as a reference. We obtained atmospheric parameters (Teff , log g, and t) to be (8025 K, 1.0 and 10 km s ) and (8050 K, 1.0 and 7 km s ) for Aur and HD 81471, respectively. The abundances of Mg, Si, S, Ca, Sc, Ti, Cr, and Fe were very close to the solar abundances in both stars. Light elements C and O were under-abundant, while N and Na were over-abundant in both stars, after correcting for non-LTE effects. Definite under-abundances of Sr were detected in both stars. Slight, but definite, over-abundances were found in Aur for the s-process elements Y, Zr, and Ba, when compared with the results of HD 81471. Enhancements in the abundances of N, Na, and s-process elements might indicate the occurences of thermal dredge-up and the s-process nucleosynthesis in Aur during the past evolution.

We report the discovery of a cool metal-poor, main-sequence star exhibiting large excesses of r-process elements. This star is one of two newly discovered cool subdwarfs (effective temperatures of 5000 K) with extremely low metallicity ([Fe/H], Comment: 16 pages, 3 figures, 2 tables, ApJL in press

Recently, many superflares on solar-type stars have been discovered as white-light flares (WLFs). The statistical study found a correlation between their energies ($E$) and durations ($\tau$): $\tau \propto E^{0.39}$ (Maehara et al. 2017 $EP\& S$, 67, 59), similar to those of solar hard/soft X-ray flares: $\tau \propto E^{0.2-0.33}$. This indicates a universal mechanism of energy release on solar and stellar flares, i.e., magnetic reconnection. We here carried out a statistical research on 50 solar WLFs observed with \textit{SDO}/HMI and examined the correlation between the energies and durations. As a result, the $E$--$\tau$ relation on solar WLFs ($\tau \propto E^{0.38}$) is quite similar to that on stellar superflares ($\tau \propto E^{0.39}$). However, the durations of stellar superflares are one order of magnitude shorter than those expected from solar WLFs. We present the following two interpretations for the discrepancy. (1) In solar flares, the cooling timescale of WLFs may be longer than the reconnection one, and the decay time of solar WLFs can be elongated by the cooling effect. (2) The distribution can be understood by applying a scaling law ($\tau \propto E^{1/3}B^{-5/3}$) derived from the magnetic reconnection theory. In this case, the observed superflares are expected to have 2-4 times stronger magnetic field strength than solar flares., Comment: 43 pages, 15 figures, accepted for publication in ApJ

We have determined the isotopic abundance ratio of 7Li/6Li in the interstellar media (ISMs) along lines of sight to HD169454 and HD250290 using the High-Dispersion Spectrograph on the Subaru Telescope. We also observed ζ Oph for comparison with previous data. The observed abundance ratios were 7Li/6Li = 8.1+3.6 –1.8 and 6.3+3.0 –1.7 for HD169454 and HD250290, respectively. These values are in reasonable agreement with those observed previously in the solar neighborhood ISMs within ±2σ error bars and are also consistent with our measurement of 7Li/6Li = 7.1+2.9 –1.6 for a cloud along the line of sight to ζ Oph. This is good evidence for homogeneous mixing and instantaneous recycling of the gas component in the Galactic disk. We also discuss several source compositions of 7Li, Galactic cosmic-ray interactions, stellar nucleosynthesis, and big bang nucleosynthesis.

The local thermodynamic equilibrium (LTE) abundances of zinc (Zn) of our sample of 35 metal-poor stars were explored in the range of � 3.0 � 0.5. This trend is better explained by a chemical evolution model constructed with models of normal SNe II, HNe, and SNe Ia, in which the metallicity effect and the single-degenerate scenario of the SNe Ia model are incorporated.

The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off stars are determined from high-resolution spectroscopy. Five of them are selected from the SDSS/SEGUE sample of metal-poor stars. The effective temperatures of these objects are all higher than 6000 K, while their metallicities, parametrized by [Fe/H], are all below -2. Six of our program objects exhibit high abundance ratios of barium ([Ba/H]> +1), suggesting large contributions of the products of former AGB companions via mass transfer across binary systems. Combining our results with previous studies provides a total of 20 CEMP main-sequence turn-off stars for which the abundances of carbon and at least some neutron-capture elements are determined. Inspection of the [C/H] ratios for this sample of CEMP turn-off stars show that they are generally higher than those of CEMP giants; their dispersion in this ratio is also smaller. We take these results to indicate that the carbon-enhanced material provided from the companion AGB star is preserved at the surface of turn-off stars with no significant dilution. In contrast, a large dispersion in the observed [Ba/H] is found for the sample of CEMP turn-off stars, suggesting that the efficiency of the s-process in very metal-poor AGB stars may differ greatly from star to star. Four of the six stars from the SDSS/SEGUE sample exhibit kinematics that are associated with membership in the outer-halo population, a remarkably high fraction.

The metallicities and abundance ratios, [X/Fe], of 12 elements—C, Na, Mg, Si, S, Ca, Ti, Cr, Ni, Y, Zr, and Ce—are determined for 14 old and 24 young metal-rich stars based on high resolution, high S/N spectra obtained with the HIDES spectrograph attached to the 1.88 m telescope of Okayama Astrophysical Observatory (Okayama, Japan). The results show that there is no any significant difference in the [X/Fe] versus [Fe/H] trend for these elements between the two groups of stars. This is consistent with the kinematics of the two groups of stars being similar to that of the thin disk. In connection with the abundance analysis, we found that iron abundances from Fe II lines are generally higher than those from Fe I lines for cool metal-rich stars. In particular, the [S/Fe] ratio strongly depends on stellar temperature. In view of this, the chemical evolution of the element sulfur can only be traced by selecting solar-type stars within a critically narrow temperature range. Inspecting a large sample of metal-rich stars, we found that young metal-rich stars generally have kinematics similar to that of the local thin disk, while old metal-rich stars show two different kinematic distributions, one with V LSR ~ −10kms−1 and the other with V LSR ~ −50kms−1. Abundances of this new population of old metal-rich stars with a slight lag in the Galactic rotation have already been investigated by the present authors. We compared the abundance patterns for the three groups of metal-rich stars, and did not find any significant difference in abundance ratios for the elements investigated. These results indicate an inhomogeneous metallicity enhancement but similar nucleosynthesis history for the Galactic evolution of the thin disk from the beginning to the present.

We obtained a high resolution, high signal-to-noise UV-blue spectrum of the extremely metal-poor red giant HD88609 to determine the abundances of heavy elements. Nineteen neutron-capture elements are detected in the spectrum. Our analysis revealed that this object has large excesses of light neutron-capture elements while heavy neutron-capture elements are deficient. The abundance pattern shows a continuously decreasing trend, as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements. Such an abundance pattern is very similar to that of HD122563 that was studied by our previous work. The results indicate that the abundance pattern found in the two stars could represent the pattern produced by the nucleosynthesis process that provided light neutron-capture elements in the very early Galaxy., Comment: 18 pages, 6 figures, accepted for publication in ApJ

A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H]=-2.7) star BS16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD122563 indicates excesses of O, Na, Mg, Al, and Sc in BS16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS22949-037 and CS29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the alpha elements. No established nucleosynthesis model exists that explains the observed abundance pattern of BS16934-002. A supernova model, including mixing and fallback, assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS16934-002., Comment: 34 pages, 4 tables, 7 figures, Astrophysical Jounal, in press

Context. It is known that the surface lithium abundances of field solar-analog G dwarfs show a large dispersion of >2 dex (among which our Sun is located at the lower end) despite the similarity of stellar parameters, and planet-host stars tend to show comparatively lower Li abundances in the narrow Teff range. Aims. To investigate the reason for these phenomena, an extensive study of Li abundances and their dependence on stellar parameters was carried out for a homogeneous sample of 118 selected solar analogs based on high-dispersion spectra obtained at Okayama Astrophysical Observatory. Methods. The atmospheric parameters were spectroscopically determined by using the equivalent widths of Fe i and Fe ii lines, the ages/masses were estimated from stellar evolutionary tracks, and the width of the macrobroadening (rotation plus macroturbulence) function as well as Li abundances (ALi) were established by spectrum-fitting analyses. Results. The resulting ALi vs. Teff relation revealed a characteristic inverse-triangle-like distribution enclosed by two clear-cut boundaries (the slanted one running from ∼5900 K to ∼5800 K and the vertical one at ∼5700 K), while the Sun is located around its lowest apex. More significantly, ALi in this region of large dispersion was found to closely correlate with the macrobroadening width (vr+m), which is considered to be the most important parameter. Conclusions. With a reasonable assumption that the difference of rotational velocity is mainly responsible for the variety of vr+m ,w e may conclude that the stellar angular momentum plays the decisive role in determining the surface Li abundances of solar-analog stars in the Teff range of ∼5900–5700 K. The low-Li tendency of planet-host stars may thus be interpreted in terms of rotational characteristics.

We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite-plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements. Several potential enrichment scenarios are presented. The low neutron-capture elements, including Sr, Ba, and Pb, suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single hypernova is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population III object and a normal Type II SN. These scenarios provide important information on the C production in the early Universe, and on the formation of C-rich stars in the early Galaxy., Comment: 35 pages (emulateapj text + 16 figures), accepted for publication in ApJ