Abstract
We report on multicolor photometry of the short-period dwarf nova CSS130418:174033+414756 during the 2013 superoutburst. The system showed an unusually short superhump period of 0.046346(67) ...d during stage A, which is one of the shortest periods among dwarf novae below the period minimum. We found that the bluest peaks in g΄ − Ic color variations tended to coincide with the brightness minima of the superhump modulations. We also studied nightly-averaged superhump amplitudes in the g΄, Rc, and Ic bands and found that they have less dependence on wavelength. These properties are likely to be in common with dwarf novae exhibiting superhumps. We successfully obtained g΄ − Rc and Rc − Ic colors during the temporal dip. The color indices were significantly bluer compared with other dips of WZ Sge-type dwarf novae. By using the period of the growing superhumps, we estimated the mass ratio to be q = 0.077(5), which is much larger than the previous study.
Abstract
The LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its ...relatively small localization skymap (71 deg
2
for a 90% credible region; revised to 50 deg
2
in GWTC-3), we performed target-of-opportunity observations using the Subaru/Hyper Suprime-Cam (HSC) in the
r
2 and
z
bands. Observations were conducted on 2020 February 25 and 28 and March 23, with the first epoch beginning 12.3 hr after the GW detection. The survey covered the highest-probability sky area of 56.6 deg
2
, corresponding to a 91% probability. This was the first deep follow-up (
m
r
≳ 24,
m
z
≳ 23) for a binary-black hole merger covering >90% of the localization. By performing image subtraction and candidate screening including light-curve fitting with transient templates and examples, we found 22 off-nucleus transients that were not ruled out as the counterparts of GW200224_222234 with our Subaru/HSC data alone. We also performed GTC/OSIRIS spectroscopy of the probable host galaxies for five candidates; two are likely to be located within the 3D skymap, whereas the others are not. In conclusion, 19 transients remain as possible optical counterparts of GW200224_222234; but we could not identify a unique promising counterpart. If there are no counterparts in the remaining candidates, the upper limits of the optical luminosity are
ν
L
ν
<
5.2
−
1.9
+
2.4
×
10
41
erg s
−1
and
ν
L
ν
<
1.8
−
0.6
+
0.8
×
10
42
erg s
−1
in the
r
2 and
z
bands, respectively, at ∼12 hr after GW detection. We also discuss improvements in the strategies of optical follow-ups for future GW events.
Nonvariable OH/IR stars are thought to have just left the asymptotic giant branch (AGB) phase. In this conventional picture, they must still show strong circumstellar extinction caused by the dust ...ejected during the AGB phase, and the extinction is expected to decrease over time because of the dispersal of the circumstellar dust after the cessation of stellar mass loss. The reduction of extinction makes the stars become apparently brighter and bluer with time, especially in the near-infrared (NIR) range. We look for such long-term brightening of nonvariable OH/IR stars by using 2MASS, UKIDSS, and OAOWFC survey data. As such, we obtain multiepoch NIR data taken over a 20 yr period (1997-2017) for 6 of 16 nonvariable OH/IR stars, and all 6 objects are found to be brightening. The K-band brightening rate of five objects ranges from 0.010 to 0.130 mag yr−1, which is reasonably explained with the conventional picture. However, one OH/IR star, OH 31.0−0.2, shows a rapid brightening, which cannot be explained only by the dispersal of the dust shell. Multicolor (J-, H-, and K-band) data are obtained for three objects, OH 25.1−0.3, OH 53.6−0.2, and OH 77.9+0.2. Surprisingly, none of them appears to have become bluer, and OH 53.6−0.2 is found to have reddened at a rate of 0.013 mag yr−1 in (J - K). Our findings suggest other mechanisms such as rapid changes in stellar properties (temperature or luminosity) or a generation of a new batch of dust grains.
Abstract
We report on multicolor photometry of WZ Sge-type dwarf novae HV Vir and OT J012059.6+325545 during superoutbursts. These systems show early superhumps with mean periods of 0.057093(45) d ...for HV Vir and 0.057147(15) d for OT J012059.6+325545. The observed early superhumps showed a common feature that the brightness minima corresponded to the bluest peaks in color variations, which may be a ubiquitous phenomenon among early superhumps of WZ Sge-type dwarf novae. We confirmed that the amplitudes of early superhumps depend on wavelength: amplitudes with longer bandpass filters show larger values. This indicates that the light source of early superhumps is generated at the outer region of the vertically extended accretion disk. On the other hand, amplitudes of ordinary superhumps are likely to be independent of wavelength. This implies that the superhump light source is geometrically thin. We also examined color variations of ordinary superhumps and found that the bluest peaks in g΄ − Ic tend to coincide with the brightness minima, particularily in stage B superhumps. This may reflect that the pressure effect plays a dominant role during stage B superhumps.
We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17-18 at phase angles of = 52 1-53 1. Additionally, we ...obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the RC and 3%-18% in the IC bands, depending on the position in the coma. We derive the "gas-free dust polarization degrees" of 13.8% 1.0% in the RC and 12.5% 1.1% in the IC bands and a gray polarimetric color, i.e., −8.7% 9.9% m−1 in optical and 1.6% 0.9% m−1 in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the RC-band polarization degree of the southeast dust tail, which consists of large dust particles (100 m-1 mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.
Abstract
In the 1–2.5 μm range, spectroscopic observations are made on the AcuA-spec asteroids, the spectra of which were obtained in a continuous covered mode between 2.5–5.0 μm by AKARI. Based on ...the Bus–DeMeo taxonomy (DeMeo et al. 2009, Icarus, 202, 160), all the AcuA-spec asteroids are classified, using both published and our observational data. Additionally, taking advantage of the Bus–DeMeo taxonomy characteristics, we constrain the characteristic of each spectral type by combining the taxonomy results with the other physical observational data from colorimetry, polarimetry, radar, and radiometry. As a result, it is suggested that certain C-, Cb-, B-type, dark X-, and D-complex asteroids have spectral properties compatible with those of anhydrous interplanetary dust particles with tiny bright material, such as water ice. This supports the proposal regarding the C-complex asteroids (Vernazza et al. 2015, ApJ, 806, 204; 2017, AJ, 153, 72). A combination of the Bus–DeMeo taxonomy for AcuA-spec asteroids with other physical clues, such as the polarimetric inversion angle, radar albedo, and mid-infrared spectroscopic spectra, will be beneficial for surface material constraints from the AcuA-spec asteroid observations.
Okayama Astrophysical Observatory Wide-Field Camera Yanagisawa, Kenshi; Shimizu, Yasuhiro; Okita, Kiichi ...
Publications of the Astronomical Society of Japan,
12/2019, Letnik:
71, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Abstract
We report on the development of a wide-field near-infrared (0.9–2.5$\, \mu$m) camera built as a renewal of the existing classical Cassegrain 0.91 m telescope at Okayama Astrophysical ...Observatory. The optics system was replaced with fast hybrid optics (f/2.5) composed of forward Cassegrain optics and quasi-Schmidt optics, which results in an effective image circle of 52 mm diameter on the focal plane. The new camera, called the Okayama Astrophysical Observatory Wide-Field Camera (OAOWFC), has imaging capabilities in the $Y$, $J$, $H$, and $K_{\rm s}$ bands over a field of view of $0.^{\!\!\!\circ }47 \times 0.^{\!\!\!\circ }47$ with a HAWAII-1 HgCdTe PACE focal plane array. The primary purpose of OAOWFC is to search for variability in the Galactic plane in the $K_{\rm s}$ band and to promptly follow up transients. We have demonstrated a photometric repeatability of 2% in the densest field in the northern Galactic plane and successfully discovered previously unreported variable stars. The observations of OAOWFC are fully autonomous, and we started scientific operations in 2015 April.
ABSTRACT Multiple outbursts of a Jupiter-family comet (JFC), 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 1110 180 m s−1 and 570 40 m s−1 at a heliocentric distance of 1.0 au. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity βmax = 1.6 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 108-109 kg of dust particles (assumed to be 0.3 m-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−1) 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 JFCs and Encke-type comets into interplanetary space at a rate of ∼10 kg s−1 or more.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We present optical (g' R sub(c) and I sub(c)) to near-infrared (J) simultaneous photometric observations for a primary transit of ...GJ3470b, a Uranus-mass transiting planet around a nearby M dwarf, by using the 50 cm MITSuME telescope and the 188 cm telescope, both at the Okayama Astrophysical Observatory. From these data, we derive the planetary mass, radius, and density as 14.1 + or - 1.3 M sub(+ in circle), ..., and 0.94 + or - 0.12 g cm super(-3), respectively, thus confirming the low density that was reported by Demory et al. based on the Spitzer/IRAC 4.5 mum photometry (... g cm super(-3)). Although the planetary radius is about 10% smaller than that reported by Demory et al., this difference does not alter their conclusion that the planet possesses a hydrogen-rich envelope whose mass is approximately 10% of the planetary total mass. On the other hand, we find that the planet-to-star radius ratio (Rp/Rs) in the J band (...) is smaller than that in the I sub(c) (0.0802 + or - 0.0013) and 4.5 mum (...) bands by 5.8% + or - 2.0% and 2.9% + or - 1.1%, respectively. A plausible explanation for the differences is that the planetary atmospheric opacity varies with wavelength due to absorption and/or scattering by atmospheric molecules. Although the significance of the observed Rp/Rs variations is low, if confirmed, this fact would suggest that GJ3470b does not have a thick cloud layer in the atmosphere. This property would offer a wealth of opportunity for future transmission-spectroscopic observations of this planet to search for certain molecular features, such as H sub(2)O, CH sub(4), and CO, without being prevented by clouds.
Abstract
We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from −11 to +140 d after the date of its B-band maximum in the optical and ...near-infrared (NIR) wavelengths conducted through the OISTER ToO (Optical and Infrared Synergetic Telescopes for Education and Research Target of Opportunity) 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 further support to the nature of SN 2012dn as an SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from 30 d after the B-band maximum. The H- and K
s-band light curves exhibited much later maximum dates at 40 and 70 d 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 an NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to 4.8–6.4 × 10−2 pc. No emission lines were found in its early phase spectra, suggesting that the ejecta–circumstellar material 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
⊙ 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.
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