V1647 Orionis (IRAS 05436-0007) : A New Look at McNeil's Nebula

We present a study of the newly discovered McNeil's nebula in Orion using the JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen extending toward north and south from the NIR source (V1647 Orionis) that illuminates McNeil's nebula. The compact nebula has an apparent diameter of about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure with two rims extending toward north-east and north-west. The north-east rim is brighter and sharp, while the north-west rim is diffuse. The north-east rim can be traced out to ~ 40 arcsec from the location of the NIR source. In contrast, no cavity structure is seen toward the south, although diffuse nebula is extended out to ~ 20 arcsec. New NIR photometric data show a significant variation in the magnitudes (> 0.15 mag) of the source of McNeil's nebula within a period of one week, that is possibly under the phase of eruptive variables like FUors or EXors.Comment: 13 pages, 5 figures in JPEG format. Accepted for the publication in PASJ Letter

Emergent Nodal Excitations due to the Coexistence of Superconductivity and Antiferromagnetism: Cases with and without Inversion Symmetry

We argue the emergence of nodal excitations due to the coupling with static antiferromagnetic order in fully-gapped superconducting states in both cases with and without inversion symmetry. This line node structure is not accompanied with the sign change of the superconducting gap, in contrast to usual unconventional Cooper pairs with higher angular momenta. In the case without inversion symmetry, the stability of the nodal excitations crucially depends on the direction of the antiferromagnetic staggered magnetic moment. A possible realization of this phenomenon in CePt$_3$Si is discussed.Comment: 4 pages, 7 figure

Strong-Coupling Superconductivity of CeIrSi3_3 with the Non-centrosymmetric Crystal Structure

We studied the pressure-induced superconductor CeIrSi$_3$ with the non-centrosymmetric tetragonal structure under high pressure. The electrical resistivity and ac heat capacity were measured in the same run for the same sample. The critical pressure was determined to be $P_{\rm c}$ = 2.25 GPa, where the antiferromagnetic state disappears. The heat capacity $C_{\rm ac}$ shows both antiferromagnetic and superconducting transitions at pressures close to $P_{\rm c}$. On the other hand, the superconducting region is extended to high pressures of up to about 3.5 GPa, with the maximum transition temperature $T_{\rm sc}$ = 1.6 K around $2.5-2.7$ GPa. At 2.58 GPa, a large heat capacity anomaly was observed at $T_{\rm sc}$ = 1.59 K. The jump of the heat capacity in the form of ${\Delta}{C_{\rm ac}}/C_{\rm ac}(T_{\rm sc})$ is 5.7 $\pm$ 0.1. This is the largest observed value among previously reported superconductors, indicating the strong-coupling superconductivity. The electronic specific heat coefficient at $T_{\rm sc}$ is, however, approximately unchanged as a function of pressure, even at $P_{\rm c}$.Comment: This paper will be published in J. Phys. Soc. Jpn. on the August issue of 200

Molecular hydrogen jets and outflows in the Serpens south filamentary cloud

We aimed to map the jets and outflows from the Serpens South star forming region and find an empirical relationship between the magnetic field and outflow orientation. Near-infrared H2 v=1-0 S(1) 2.122{\mu}m -line imaging of the \sim 30'-long filamentary shaped Serpens South star forming region was carried out. K s broadband imaging of the same region was used for continuum subraction. Candidate driving sources of the mapped jets/outflows are identified from the list of known protostars and young stars in this region, which was derived from studies using recent Spitzer and Herschel telescope observations. 14 Molecular Hydrogen emission-line objects(MHOs) are identified using our continuum-subtracted images. They are found to constitute ten individual flows. Out of these, nine flows are located in the lower-half(southern) part of the Serpens South filament, and one flow is located at the northern tip of the filament. Four flows are driven by well-identified Class 0 protostars, while the remaining six flows are driven by candidate protostars mostly in the Class I stage, based on the Spitzer and Herschel observations. The orientation of the outflows is systematically perpendicular to the direction of the near-infrared polarization vector, recently published in the literature. No significant correlation was observed between the orientation of the flows and the axis of the filamentary cloud.Comment: Accepted by A&A for publication. 7 pages, 5 figure

Nonuniform Spin Triplet Superconductivity due to Antisymmetric Spin-Orbit Coupling in Noncentrosymmetric Superconductor CePt3_3Si

We show that the nonuniform state (Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state) of the spin triplet superconductivity in noncentrosymmetric systems is stabilized by antisymmetric spin-orbit coupling even if the magnetic field is absent. The transition temperature of the spin triplet superconductivity is reduced by the antisymmetric spin-orbit coupling in general. This pair breaking effect is shown to be similar to the Pauli pair breaking effect due to magnetic field for the spin singlet superconductivity, in which FFLO state is stabilized near the Pauli limit (or Chandrasekhar-Clogston limit) of external magnetic field. Since there are gapless excitations in nonuniform superconducting state, some physical quantities such as specific heat and penetration depth should obey the power low temperature-dependences. We discuss the possibility of the realization of nonuniform state in CePt$_3$Si.Comment: 8 pages, 6 figure

Wide-Field Survey of Emission-line Stars in IC 1396

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg^2 and their i'-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) color-color diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected color-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.Comment: 48 pages, 12 figures, 5 tables, accepted for publication in A

Thermodynamic Studies on Non Centrosymmetric Superconductors by AC Calorimetry under High Pressures

We investigated the non centrosymmetric superconductors CePt$_3$Si and UIr by the ac heat capacity measurement under pressures. We determined the pressure phase diagrams of these compounds. In CePt$_3$Si, the N\'{e}el temperature $T_{\rm N}$ = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure $P_{\rm AF}$ $\simeq$ 0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to $P_{\rm AF}$ $\simeq$ 1.5 GPa. The phase diagram of CePt$_3$Si is very unique and has never been reported before for other heavy fermion superconductors. In UIr, the heat capacity shows an anomaly at the Curie temperature $T_{\rm C1}$ = 46 K at ambient pressure, and the heat capacity anomaly shifts to lower temperatures with increasing pressure. The present pressure dependence of $T_{\rm C1}$ was consistent with the previous studies by the resistivity and magnetization measurements. Previous ac magnetic susceptibility and resistivity measurements suggested the existence of three ferromagnetic phases, FM1-3. $C_{\rm ac}$ shows a bending structure at 1.98, 2.21, and 2.40 GPa .The temperatures where these anomalies are observed are close to the phase boundary of the FM3 phase.Comment: This paper was presented at the international workshop ``Novel Pressure-induced Phenomena in Condensed Matter Systems(NP2CMS)" August 26-29 2006, Fukuoka Japa

Microscopic Mechanism and Pairing Symmetry of Superconductivity in the Noncentrosymmetric Heavy Fermion Systems CeRhSI3_3 and CeIrSi3_3

We study the pairing symmetry of the noncentrosymmetric heavy fermion superconductors CeRhSi$_3$ and CeIrSi$_3$ under pressures, which are both antiferromagnets at ambient pressure. We solve the Eliashberg equation by means of the random phase approximation and find that the mixed state of extended s-wave and p-wave rather than the $d+f$ wave state could be realized by enhanced antiferromagnetic spin fluctuations. It is elucidated that the gap function has line nodes on the Fermi surface and the resulting density of state in the superconducting state shows a similar character to that of usual d-wave superconductors, resulting in the NMR relaxation rate $1/(T_1T)$ that exhibits no coherence peak and behaves like $1/(T_1T)\propto T^2$ at low temperatures

Star Formation and Young Population of the HII Complex Sh2-294

The Sh2-294 HII region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in the region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 HII region at 3.6, 4.5, 5.8, and 8.0 microns observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 microns) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the HII region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (< 4 solar masses) YSOs; however, we also detected a massive YSO (~9 solar masses) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed younger population of the region relative to Class II sources (age ~ 4.5 x 10^6 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the HII region powered by a ~ 4 x 10^6 yr B0 main-sequence star.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in The Astrophysical Journa

Anomalous Spin Response in Non-centrosymmetric Compounds

We examine static spin susceptibilities $\chi_{\alpha\beta}({\bf q})$ of spin components $S_{\alpha}$ and $S_{\beta}$ in the non-centrosymmetric tetragonal system. These show anomalous momentum dependences like $\chi_{xx}({\bf q})-\chi_{yy}({\bf q})\sim q_x^2-q_y^2$ and $\chi_{xy}({\bf q})+\chi_{yx}({\bf q})\sim q_x q_y$, which vanish in centrosymmetric systems. The magnitudes of the anomalous spin susceptibilities are enhanced by the on-site Coulomb interaction, especially, around an ordering wave vector. The significant and anomalous momentum dependences of these susceptibilities are explained by a group theoretical analysis. As the direct probe of the anomalous spin susceptibility, we propose a polarized neutron scattering experiment.Comment: 4 pages, 1 table, 4 figure