bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral Evolution of the GRB 030329 Afterglow: Detection of the Supernova Nebular Phase Emissions
Authors: Kosugi George , Mizumoto Yoshihiko , Kawai Nobuyuki , Yoshida Atsumasa , Kawabata Koji S. , Totani Tomonori , Iye Masanori , Sekiguchi Kazuhiro , Aoki Kentaro , Ohyama Youichi , Aoki Wako , Kobayashi Naoto , Komiyama Yutaka , Noumaru Jun’ichi , Ogasawara Ryusuke , Sakamoto Takanori , Shirasaki Yuji , Takata Tadafumi , Tamagawa Toru , Torii Ken’ichi , Urata Yuji , Watanabe Jun-ichi , Yamada Toru , Qiu Yulei 
Published: March 2014

Abstract
GRB 030329 is the first Gamma-ray burst event for which a connection with a supernova (SN 2003dh) has been confirmed spectroscopically in its early phase. We present optical spectroscopy of this object 40 and 85 days after the burst (35 and 73 rest-frame days, respectively) obtained with the Subaru 8.2-m telescope. After subtracting the host galaxy template spectrum, the second-epoch spectrum shows nebular-phase emission lines emerging from the dominated photospheric-phase spectrum. The transition from the photospheric phase to the nebular phase has just started, or was slowly progressing at the time of our second-epoch observations. Our spectral analysis of the nebular-phase emission lines suggests that the explosion of the progenitor of the GRB 030329 was aspherical, and that the axis of an asphericity is well aligned to both the GRB relativistic jet and our line of sight. Although the decay index and the color evolution in the rest frame during our two epochs are very consistent with those of the Type Ic supernovae SN 1998bw and SN 1997ef, the nebular-phase lines emerged slightly earlier than in the case of these supernovae. These results infer that the most important factor that distinguishes SNe with GRB from SNe without GRB is the scale of the jet activity, or a viewing-angle effect, or both of them.
13CO (J=1–0) Survey of Molecular Clouds toward the Monoceros and Canis Major Region
Authors: Kim Bong Gyu , Kawamura Akiko , Yonekura Yoshinori , Fukui Yasuo 
Published: March 2014

Abstract
Through a large-scale ${{13\atop} \mathrm{CO}}$ ($J = 1 \hbox{--} 0$) survey toward a region in Monoceros and Canis Major, we present following results: (1) We identified in total 115 clouds. (2) Group I (CMa OB1 and G220.8$-$1.7) may physically connected with Group II (Mon R2 and NGC 2149). (3) 496 YSO candidates were chosen from IRAS point source catalog (IPC). (4) The mass spectrum of the Local clouds shows a power-law relation with an index of $-1.55 \pm 0.09$. (5) The number fraction of star-forming clouds increases as the cloud mass increases. Especially, massive clouds of $M_\mathrm{cloud} \ge 10^{3.5} \,{{{M}_{\odot}}}$ are all star-forming clouds. (6) The line width–cloud radius relation is best fitted as $\Delta V_\mathrm{comp} \propto r_\mathrm{cloud}^{0.47}$ ($\mbox{correlation coefficient} = 0.87$ correlation coefficient$= 0.87$). (7) The distribution of $(M_\mathrm{vir} / M_\mathrm{cloud})$ shows that star-forming clouds tend to be more virialized than no star-forming clouds. (8) Star formation in Group I is more active than that in Group II. (9) Unexpected small number of low-mass clouds in Group I may be due to strong UV radiation from O-type stars in the vicinity of the clouds. (10) Star formation in Group II might occurred by self-gravitational, except for the most massive cloud.
Chandra Observation of Luminous Sources in the Nearby Irregular Galaxy NGC 4449
Authors: Miyawaki Ryohei , Sugiho Masahiko , Kokubun Motohide , Makishima Kazuo 
Published: March 2014

Abstract
Using archival Chandra ACIS-S data, $0.5 \hbox{--} 8.0 \,\mathrm{keV}$ X-ray spectra of two luminous X-ray sources in the nearby dwarf irregular galaxy NGC 4449 were studied. One, with an extremely high luminosity of $1.3 \times 10^{39} \;\mathrm{erg} \,\mathrm{s}^{-1}$ in the $0.5 \hbox{--} 8.0 \;\mathrm{keV}$ band, shows a spectrum that is well described with a power-law model of photon index $\sim 2$. Its properties are consistent with those of ultraluminous compact X-ray sources observed in nearby galaxies. The spectrum of the other, with a luminosity of $2.7 \times 10^{38} \,\mathrm{erg} \,\mathrm{s}^{-1}$ in the same band, is successfully represented with a so-called multi-color disk blackbody emission model with an inner-most disk temperature of $\sim 0.59 \,\mathrm{keV}$. Its spectral parameters are typical of ordinary black hole binaries observed in our Galaxy and the Large Magellanic Cloud. These young population objects, together with a bright supernova remnant and diffuse hot gas already reported, suggest that the X-ray emission from irregular galaxies is generally enhanced by their recent star-forming activities.
A Subaru Search for Lyman$\alpha$
Emitters at
z
= 5.8 with an Intermediate-Band Filter
Authors: Ajiki Masaru , Taniguchi Yoshiaki , Fujita Shinobu S. , Shioya Yasuhiro , Nagao Tohru , Murayama Takashi , Yamada Sanae F. , Umeda Kazuyoshi , Sasaki Shunji S. , Sumiya Ryoko , Komiyama Yutaka 
Published: March 2014

Abstract
We present the results of a survey for Ly $\alpha$ emitters at $z \approx 5.8$ using a new intermediate-band filter centered at $\lambda_\mathrm{c} \approx 8275 \,{Å$ with $\Delta\lambda_\mathrm{FWHM} \approx 340 \,{Å$ (i.e., spectroscopic resolution is $R \approx 24$ ) and a combination with a traditional narrow-band centered at $\lambda_\mathrm{c} \approx 8150 \,{Å$ with $\Delta\lambda_\mathrm{FWHM} \approx 120 \,{Å$ ( $R \approx 68$ ). Our observations were made using the Subaru Prime Focus Camera, Suprime-Cam, on the 8.2m Subaru telescope in a sky area surrounding the high-redshift quasar SDSSp J104433.04 $-$ 012522.2 at $z = 5.74$ , covering an effective sky area of $\approx 720 \;\mathrm{arcmin}^2$ . In this survey, we have found four Ly $\alpha$ -emitter candidates from the intermediate-band image ( $z \approx 5.8$ with $\Delta z \approx 0.3$ ). Combined with our previous results based on the NB816 imaging, we discuss the star-formation activity in galaxies between $z \approx 5.7$ and $z \approx 5.9$ .
SiO Maser Survey of IRAS Sources in the Inner Galactic Disk
Authors: Deguchi Shuji , Fujii Takahiro , Glass Ian S. , Imai Hiroshi , Ita Yoshifusa , Izumiura Hideyuki , Kameya Osamu , Miyazaki Atsushi , Nakada Yoshikazu , Nakashima Jun-ichi 
Published: March 2014

Abstract
We surveyed 401 color-selected IRAS sources in the galactic disk in the SiO $J = 1 \hbox{--} 0, v = 1$ and 2 maser lines at 43 GHz, resulting in 254 (239 new) detections. The observed sources lie mostly in a strip of the inner galactic disk with boundaries $-10^{\circ} &lt; l &lt; 40^{\circ}$ and $\vert b\vert &lt; 3^{\circ}$. This survey provides radial velocities of inner-disk stars for which optical measurements cannot be made due to interstellar extinction. The SiO $l \hbox{--} v$ diagram in the area $-10^{\circ} &lt; l &lt; 40^{\circ}$ exhibits fewer objects coincident with the molecular ring feature than does the OH 1612 MHz source $l \hbox{--} v$ map, indicating a slight difference of stellar type between SiO and OH emitting stars. After identifying all of the SiO detected sources in the 2MASS near-infrared catalog, we computed their luminosity distances based on the infrared fluxes. We then mapped these objects onto the first quadrant of the galactic plane. Combining the distances with the SiO radial velocities, we obtained a pattern speed for SiO maser sources, $\Omega_{\mathrm{P}} = 21 (\pm 13) \,\mathrm{km} \,\mathrm{s}^{-1} \,\mathrm{kpc}^{-1}$, between the distances 1 and 5.5 kpc, without the use of any dynamical models. The increase of the pattern speed toward the galactic center (up to $60 \,\mathrm{km} \,\mathrm{s}^{-1} \,\mathrm{kpc}^{-1}$ between the distances, 5.5 and 7 kpc) suggests the presence of two pattern speeds in the Galaxy.
Locating the Warm–Hot Intergalactic Medium in the Simulated Local Universe
Authors: Yoshikawa Kohji , Dolag Klaus , Suto Yasushi , Sasaki Shin , Yamasaki Noriko Y. , Ohashi Takaya , Mitsuda Kazuhisa , Tawara Yuzuru , Fujimoto Ryuichi , Furusho Tae , Furuzawa Akihiro , Ishida Manabu , Ishisaki Yoshitaka , Takei Yoh 
Published: March 2014

Abstract
We present an analysis of mock spectral observations of warm–hot intergalactic medium (WHIM) using a constrained simulation of the local universe. The simulated map of oxygen emission lines from local WHIM well reproduces the observed structures traced by galaxies in the real local universe. We further attempt to perform mock observation of the outer parts of the simulated Coma cluster and A 3627 adopting the expected performance of DIOS (Diffuse Intergalactic Oxygen Surveyor), which is proposed as a dedicated soft X-ray mission to search for cosmic missing baryons. We find that WHIMs surrounding nearby clusters are detectable with a typical exposure time of one day, and thus constitute realistic and promising targets for DIOS. We also find that an X-ray emitting clump in front of Coma cluster, recently reported in the XMM-Newton observation, has a counterpart in the simulated local universe, and its observed spectrum can be well reproduced in the simulated local universe if the gas temperature is set to the observationally estimated value.
Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova, EG Cancri
Authors: Kato Taichi , Nogami Daisaku , Matsumoto Katsura , Baba Hajime 
Published: March 2014

Abstract
We report on time-resolved photometric observations of the WZ Sge-type dwarf nova, EG Cnc (Huruhata’s variable), during its superoutburst in 1996–1997. EG Cnc, after the main superoutburst accompanied by the development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a series of six major rebrightenings. During these rebrightenings and the following long fading tail, EG Cnc persistently showed superhumps having a period equal to the superhump period observed during the main superoutburst. The persistent superhumps had a constant superhump flux with respect to the rebrightening phase. These findings suggest that the superhumps observed during the rebrightening stage and the fading tail are a “remnant” of the usual superhumps, and are not newly triggered by rebrightenings. By a comparison with the 1977 outburst of this object and outbursts of other WZ Sge-type dwarf novae, we propose an activity sequence of WZ Sge-type superoutbursts, in which the current outburst of EG Cnc is placed between a single-rebrightening event and distinct outbursts separated by a dip. The post-superoutburst behavior of WZ Sge-type dwarf novae can be understood in the presence of a considerable amount of remnant matter behind the cooling front in the outer accretion disk, even after the main superoutburst. We consider that a premature quenching of the hot state due to the weak tidal effect under the extreme mass ratio of the WZ Sge-type binary is responsible for the origin of the remnant mass.
V1494 Aql: Eclipsing Fast Nova with an Unusual Orbital Light Curve
Authors: Kato Taichi , Ishioka Ryoko , Uemura Makoto , Starkey Donn R. , Krajci Tom 
Published: March 2014

Abstract
We present the time-resolved photometry of V1494 Aql (Nova Aql 1999 No. 2) between 2001 November and 2003 June. The object is confirmed to be an eclipsing nova with a period of 0.1346138(2) d. The eclipses were present in all observed epochs. The orbital light curve shows a rather unusual profile, consisting of a bump-like feature at phase 0.6–0.7 and a dip-like feature at phase 0.2–0.4. These features were probably persistently present in all available observations between 2001 and 2003. A period analysis outside of the eclipses has confirmed that these variations have a period common to the orbital period, and are unlikely to be interpreted as superhumps. We suspect that the structure (probably in the accretion disk) fixed in the binary rotational frame is somehow responsible for this feature.
Unusual State in V Sagittae
Authors: Kato Taichi 
Published: March 2014

Abstract
It has recently been demonstrated that the recurring high/low states in the peculiar binary V Sge can be explained by considering limit-cycle oscillation involving negative feedback by the wind on the mass-transfer from the secondary star. We noticed, from recent observations reported to VSNET, the presence of a different state of recurring variations (recurrence time $\sim 30 \,\mathrm{d}$), showing a gradual rise and a sudden drop in brightness. The observed features of this light variation are unlikely to be reproduced by a limit-cycle oscillation mechanism involving a mass-transfer variation from the secondary star (Hachisu, Kato 2003). We suggest that this phenomenon originates from an unidentified intrinsic instability in the disk, or in the wind of a high-luminosity object, such as in V Sge.
Deep Fading of the New Herbig Be Star MisV1147
Authors: Uemura Makoto , Kato Taichi , Ishioka Ryoko , Yoshida Seiichi , Kadota Ken-ichi , Ohkura Nobuo , Henden Arne , Pejcha Ondrej , Kinugasa Kenzo , Fujii Mitsugu , Simonsen Mike , Greaves John , Dubovsky Pavol A. , Poyner Gary , West Doug , Stine Robert J. , Taylor Dan , Poxon Michael , Muyllaert Eddy , Ripero José , Reszelski Maciej , Jones Christopher P. 
Published: March 2014

Abstract
We report on the discovery of a new variable star, MisV1147, by the MISAO Project and its unusual photometric variations. The light curve of the object is characterized by two distinct states, that is, a relatively calm, bright state and an active state during which repetitive fadings with large amplitudes of $\sim 2 \,\mathrm{mag}$ were observed. The fading events were associated with optical reddening. The object is identified with a catalogued $\mathrm{H}\alpha$ emission star, which has been confirmed by our spectroscopic observations. The $\mathrm{H}\alpha$ emission line is narrow and symmetric both in the bright and faint phases. The object has infrared colors analogous to T Tau stars or Herbig Ae/Be stars. In conjunction with the detection of a NaD absorption line and its position close to Cep OB1, we conclude that MisV1147 is a Herbig Be star with its spectral type of B2. Its optical-infrared spectral energy distribution is typical for Herbig Ae/Be stars, which supports this classification. The overall properties of the light curve are reminiscent of a UX Ori sub-group, showing Algol-type minima. The most noteworthy feature of MisV1147 is that it has a spectral type B2, whereas known UX Ori stars have spectral types later than B8. The object, furthermore, has one of the largest amplitudes of variations among known Herbig Ae/Be stars. Hence the object breaks the very strong correlation between the variation amplitude and the spectral type. This implies that dust clumps in circumstellar matter can significantly obscure a central object even in the early-type system.
Metallicities in Four Planet-Harbouring K-Type Giants: HD 47536, HD 59686, HD 137759, and HD 219449
Authors: Sadakane Kozo , Ohnishi Takashi , Ohkubo Michiko , Takeda Yoichi 
Published: March 2014

Abstract
Spectroscopic abundance analyses are carried out for four K-type giant stars that have recently been reported to be accompanied by giant planets, together with two reference stars of similar spectral types. The resulting metallicities, $\mathrm{[Fe/H]}$, for three stars (HD 59686, HD 137759, and HD 219449) coincide with the solar value, while that for HD 47536 is definitely lower than the Sun. Combining with the reported low metallicity found for the G9 III giant HD 104985 (which has a planet with an orbital period 198 days), there is no known metal-rich star with planets among giant stars. This may suggest a lower frequency of incidence of high-metallicity stars for giant stars with planets when compared with dwarf stars with planets.
High-Dispersion Spectra Collection of Nearby F–K Stars at Okayama Astrophysical Observatory: A Basis for Spectroscopic Abundance Standards
Authors: Yoichi Takeda , Sato Bun’ei , Kambe Eiji , Masuda Seiji , Izumiura Hideyuki , Watanabe Etsuji , Ohkubo Michiko , Yanagisawa Kenshi , Yasaka Yoshiro , Honda Satoshi , Kawanomoto Satoshi , Aoki Wako , Ando Hiroyasu , Sadakane Kozo , Takada-Hidai Masahide , Miyama Shoken M. 
Published: March 2014

Abstract
Towards constructing a system of high-dispersion spectroscopic standard stars with well-established abundances, so that adequate reference stars of similar properties may be found for precise differential abundance studies of any near-solar type stars, we have collected high-resolution ($R \sim 70000$) echelle spectra for 160 F–K dwarfs and subgiants of the solar neighborhood in three wavelength regions (5000–6200 Å, 5800–7000 Å, and 7600–8800 Å) at Okayama Astrophysical Observatory. This spectra database is open to the public.
The 2003 Superoutburst of an SU UMa-Type Dwarf Nova, GO Comae Berenicis
Authors: Imada Akira , Kato Taichi , Uemura Makoto , Ishioka Ryoko , Krajci Thomas , Sano Yasuo , Vanmunster Tonny , Starkey Donn R. , Cook Lewis M. , Pietz Jochen , Nogami Daisaku , Yeung Bill , Nakajima Kazuhiro , Tanabe Kenji , Koizumi Mitsuo , Taguchi Hiroki , Yamada Norimi , Nishi Yuichi , Martin Brian , Torii Ken’ichi , Kinugasa Kenzo , Jones Christopher P. 
Published: March 2014

Abstract
We photometrically observed a 2003 June superoutburst of GO Gom. The mean superhump period was 0.063059(13) d. The resultant data revealed that (1) the obtained light curve contained a precursor, (2) a plateau stage of the object lasted for 8 days, which is remarkably shorter than that of ordinary SU UMa-type dwarf novae, and (3) the amplitude of the superoutburst was less than 5 mag, which is unpredictably small when taking into account the fact that the supercycle of GO Com is about 2800 days. In order to explain these anomalies, a mass-elimination process from the accretion disk, such as evaporation, may play an important role.
Spectroscopic Study on the Atmospheric Parameters of Nearby F–K Dwarfs and Subgiants
Authors: Takeda Yoichi , Ohkubo Michiko , Sato Bun’ei , Kambe Eiji , Sadakane Kozo 
Published: March 2014

Abstract
Based on a collection of high-dispersion spectra obtained at Okayama Astrophysical Observatory, the atmospheric parameters ($T_{\mathrm{eff}}, \log g, v_{\mathrm{t}}$, and $\mathrm{[Fe/H]}$) of 160 mid-F through early-K stars were extensively determined by the spectroscopic method using the equivalent widths of Fe I and Fe II lines along with the numerical technique of Takeda et al. (2002, PASJ, 54, 451). The results are comprehensively discussed and compared with the parameter values derived by different approaches (e.g., photometric colors, theoretical evolutionary tracks, Hipparcos parallaxes, etc.) as well as with the published values found in various literature. It has been confirmed that our purely spectroscopic approach yields fairly reliable and consistent results.
Radial-Velocity Variability of G-Type Giants: First Three Years of the Okayama Planet Search Program
Authors: Sato Bun’ei , Kambe Eiji , Takeda Yoichi , Izumiura Hideyuki , Masuda Seiji , Ando Hiroyasu 
Published: March 2014

Abstract
We report on the radial-velocity variability of G-type giants based on the results of precise Doppler measurements of 57 stars that were observed for the first 3 years of the Okayama Planet Search Program. This program aims to search for planets around intermediate-mass stars in their evolved stages as late-G giants. We found that most of the targets with $B-V&lt;1.0$ have radial-velocity scatters of $\sigma \sim 10 \;\mathrm{m} \,\mathrm{s}^{-1}$, with the most stable reaching levels of $6 \hbox{--} 8 \,\mathrm{m} \,\mathrm{s}^{-1}$, while those with $B-V&gt;1.0$ typically show $\sigma \sim 20 \,\mathrm{m} \,\mathrm{s}^{-1}$. In total, about 60% of the targets are stable in radial velocity to a level of $\sigma &lt; 15 \,\mathrm{m} \,\mathrm{s}^{-1}$ over 1–3 years, and about 90% have $\sigma &lt; 30 \,\mathrm{m} \,\mathrm{s}^{-1}$. We found that 4 stars (HD 30557, HD 34559, HD 68077, and HD 85444) show significant long-term radial-velocity trends, suggesting that they are probably orbited by unseen stellar or substellar companions. Three stars (HD 79181, HD 104985, and HD 141680) show periodic radial-velocity variations. HD 104985 is the first planet-harboring star discovered from our survey. The properties of the variations in these 3 stars have been, and will be, extensively discussed in separate papers. Relatively large, but not apparently periodic, radial-velocity variations of $\sigma \gt 30 \,\mathrm{m} \,\mathrm{s}^{-1} \sigma &gt; 30 \,\mathrm{m} \,\mathrm{s}^{-1}$ are found in 4 stars (HD 41597, HD 134190, HD 161178, and HD 176598). For most of the stars without showing any significant periodicity, we can exclude companions with $K\gt50 \,\mathrm{m} \,\mathrm{s}^{-1} K&gt;50 \,\mathrm{m} \,\mathrm{s}^{-1}$, or $m_2 \sin i \gt 1.8 \,M_\mathrm{J}(a/\mathrm{AU})^{1/2}(M_{*}/{{{M}_{\odot}}})^{1/2} m_2 \sin i &gt; 1.8 \,M_\mathrm{J}(a/\mathrm{AU})^{1/2}(M_{*}/{{{M}_{\odot}}})^{1/2}$ for orbital radii $a \lesssim 1 \hbox{--} 2 \,\mathrm{AU}$.
Sulfur Abundances in Metal-Poor Stars Based on OAO-1.88 m/HIDES Spectra
Authors: Takada-Hidai Masahide , Saito Yu-ji , Takeda Yoichi , Honda Satoshi , Sadakane Kozo , Masuda Seiji , Izumiura Hideyuki 
Published: March 2014

Abstract
The LTE abundances of sulfur (S) of 21 metal-poor stars and one normal star were explored in the metallicity range of $-3 &lt; \mathrm{[Fe/H]} \leq 0$, based on the equivalent widths of the S I (1) 9212, 9237 Å and S I (6) 8693, 9894 Å lines measured on high-resolution spectra, which were observed by the OAO 1.88-m telescope equipped with HIDES. Our main results are: (1) The abundances derived from the S I (6) lines are consistent with those from the S I (1) lines among our sample stars in the range of $\mathrm{[Fe/H]} \gt-2 \mathrm{[Fe/H]} \gt-2$ with an average difference of $+0.03 \pm 0.05 \,\mathrm{dex}$, whereas a significant discrepancy is observed in the range of $\mathrm{[Fe/H]} \leq-2$. (2) The behavior of $\mathrm{[S(6)/Fe]}$ versus $\mathrm{[Fe/H]}$ of our halo sample stars exhibits a nearly flat trend with an average of $+0.62 \pm 0.09 \,\mathrm{dex}$ in the range of $-3 &lt; \mathrm{[Fe/H]} &lt;-1.25$, and shows a distribution around $+0.29 \,\mathrm{dex}$ in $-1.25 \leq\mathrm{[Fe/H]}\leq-0.7$. Our sample stars with $-1.25 \leq \mathrm{[Fe/H]} \leq-0.5$ follow an increasing trend with decreasing $\mathrm{[Fe/H]}$. The behavior of $\mathrm{[S(1)/Fe]}$ of our sample stars also shows essentially the same trend as $\mathrm{[S(6)/Fe]}$, though it is quantitatively different. (3) The S behavior in the range of $-3 &lt; \mathrm{[Fe/H]} \leq 0$ inferred from the abundances of multiplets 6 and 1 are qualitatively consistent with each other, and may be represented by a combination of a nearly flat trend and a linearly increasing trend with decreasing $\mathrm{[Fe/H]}$. A transition of the trend is likely to occur at $\mathrm{[Fe/H]} \sim-1.5 \,\mathrm{dex}$.
Core Structure of Intracluster Gas: Isothermal Hydrostatic Equilibrium
Authors: Akahori Takuya , Masai Kuniaki 
Published: March 2014

Abstract
We investigated the core structure of intracluster hot gas based on the so-called $\beta$-model. We found that the virial temperature, $T_{\mathrm{vir}}$, of a cluster may be represented better by $\beta T_{\mathrm{X}}$ than $T_{\mathrm{X}}$, where $\beta$ is a parameter obtained from the X-ray surface brightness, and $T_{\mathrm{X}}$ is the emission-weighted mean temperature of the gas. For 121 clusters observed by ROSAT and ASCA, the luminosity-temperature relation, $L_{\mathrm{X}} \hbox{--} \beta T_{\mathrm{X}}$, is found to be less steep than $L_{\mathrm{X}} \hbox{--} T_{\mathrm{X}}$. The clusters can be classified into large and small core groups, and the latter exhibits no significant correlation between the core and virial radii. We examined the properties of the small core clusters, and found that they have a shorter cooling time than the Hubble time, while no significant correlation was found with the presence of cD galaxies or asymmetry in the surface brightness. We carried out hydrodynamical calculations to simulate the $\beta$-model and confirmed the above results: $T_{\mathrm{vir}} \simeq \beta T$ for the gas temperature, $T$, and the gas core formed due to a central cD galaxy is too small to account for the cores of the smaller core clusters.