Showing papers by "Takashi J. Moriya published in 2013"
TL;DR: In this article, the early light curve of superluminous supernova 2006gy was modeled by using a one-dimensional multigroup radiation hydrodynamics code STELLA, and the initial conditions were constructed based on the shock breakout condition, assuming that the circumstellar medium is dense enough to cause the burst within it.
Abstract: We show model light curves of superluminous supernova 2006gy on the assumption that the supernova is powered by the collision of supernova ejecta and its dense circumstellar medium. The initial conditions are constructed based on the shock breakout condition, assuming that the circumstellar medium is dense enough to cause the shock breakout within it. We perform a set of numerical light curve calculations by using a one-dimensional multigroup radiation hydrodynamics code STELLA. We succeeded in reproducing the overall features of the early light curve of SN 2006gy with the circumstellar medium whose mass is about 15 Msun (the average mass-loss rate ~ 0.1 Msun/yr). Thus, the progenitor of SN 2006gy is likely a very massive star. The density profile of the circumstellar medium is not well constrained by the light curve modeling only, but our modeling disfavors the circumstellar medium formed by steady mass loss. The ejecta mass is estimated to be comparable to or less than 15 Msun and the explosion energy is expected to be more than 4e51 erg. No 56Ni is required to explain the early light curve. We find that the multidimensional effect, e.g., the Rayleigh-Taylor instability, which is expected to take place in the cool dense shell between the supernova ejecta and the dense circumstellar medium, is important in understanding supernovae powered by the shock interaction. We also show the evolution of the optical and near-infrared model light curves of high-redshift superluminous supernovae. They can be potentially used to identify SN 2006gy-like superluminous supernovae in the future optical and near-infrared transient surveys.
216 citations
TL;DR: In this article, the authors investigated the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type-Ic and showed that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SNIc.
Abstract: Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ~0.05-0.20 M ☉ of material and the formation of a low-mass neutron star (NS). We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 10–3-10–2. Finally, we argue that the second explosion in some double NS systems (for example, the double pulsar PSR J0737–3039B) was likely associated with an ultra-stripped SN Ic.
193 citations
TL;DR: In this article, an analytic model for bolometric light curves which are powered by the interaction between supernova ejecta and a dense circumstellar medium is presented, which is aimed at modelling Type IIn supernovae to determine the properties of their supernova ejecteda and circumstellar Medium.
Abstract: We present an analytic model for bolometric light curves which are powered by the interaction between supernova ejecta and a dense circumstellar medium. This model is aimed at modelling Type IIn supernovae to determine the properties of their supernova ejecta and circumstellar medium. Our model is not restricted to the case of steady mass loss and can be applied broadly. We only consider the case in which the optical depth of the unshocked circumstellar medium is not high enough to affect the light curves. We derive the luminosity evolution based on an analytic solution for the evolution of a dense shell created by the interaction. We compare our model bolometric light curves to observed bolometric light curves of three Type IIn supernovae (2005ip, 2006jd, 2010jl) and show that our model can constrain their supernova ejecta and circumstellar medium properties. Our analytic model is supported by numerical light curves from the same initial conditions.
135 citations
TL;DR: In this article, the authors investigated the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic and showed that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic.
Abstract: Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ~0.05-0.20 M_sun of material and the formation of a low-mass neutron star. We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 0.001-0.01. Finally, we argue that the second explosion in some double neutron star systems (for example, the double pulsar PSR J0737-3039B) was likely associated with an ultra-stripped SN Ic.
100 citations
TL;DR: In this article, the authors show that the spectra of the Pan-STARRS transient source are well fit by normal TypeIa supernova (SNIa) templates and the multi-band colors and lightcurve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z = 1.3883.
Abstract: Recently, Chornock and co-workers announced the Pan-STARRS discovery of a transient source reaching an apparent peak luminosity of ∼4×10 44 ergs −1 . We show that the spectra of this transient source are well fit by normal TypeIa supernova (SNIa) templates. The multi-band colors and lightcurve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z = 1.3883; however, the observed flux is a constant factor of ∼30 times too bright in each band over time as compared to the templates. At minimum, this shows that the peak luminosities inferred from the light-curve widths of some SNeIa will deviate significantly from the established, empirical relation used by cosmologists. We argue on physical grounds that the observed fluxes do not reflect an intrinsically luminous SNIa, but rather PS1-10afx is a normal SNIa whose flux has been magnified by an external source. The only known astrophysical source capable of such magnification is a gravitational lens. Given the lack of obvious lens candidates, such as galaxy clusters, in the vicinity, we further argue that the lens is a supermassive black hole or a comparatively low-mass dark matter halo. In this case, the lens continues to magnify the underlying host galaxy light. If confirmed, this discovery could impact a broad range of topics including cosmology, gamma-ray bursts, and dark matter halos. Subject headings: supernovae: individual (PS1-10afx) — gravitational lensing: strong — gravitational lensing: micro — dark matter
72 citations
TL;DR: In this article, a Monte Carlo simulation is used to construct spectra of supernovae interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum and an emission line spectrum.
Abstract: We construct spectra of supernovae interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum and an emission-line spectrum. In a Monte Carlo simulation we generate more than 800 spectra, distribute them to 10 different classifiers and study how the different simulation parameters affect the appearance of the spectra. SNe IIn showing some structure over the continuum were characterized as SNe IInS. We demonstrate that the flux ratio of the underlying SN to the continuum fv is the most important parameter determining the spectral classification. Thermonuclear SNe get progressively classified as Ia-CSM, IInS and IIn as fv decreases. The transition between Ia-CSM and IInS occurs at fv~0.2-0.3. It shown that SNe Ia-CSM are found at the magnitude range -19.5> M >-21.6, in good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association is due to a luminosity bias (91T-like being brighter than normal Ia). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors. Despite the similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was small and mostly at low S/N. Combined with the luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Ha profiles vary with fv. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A simulation including radiative transfer shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data.
61 citations
TL;DR: In this article, the authors perform detailed simulations to study the detectability of superluminous supernovae (SLSNe) at high redshifts, using the observationally-calibrated star formation rate density and supernova occurrence rate.
Abstract: Observational identification of the first stars is one of the great challenges in the modern astronomy. Although a single first star is too faint to be detected, supernova explosions of the first stars can be bright enough. An important question is whether such supernovae can be detected in the limited observational area with realistic observational resources. We perform detailed simulations to study the detectability of superluminous supernovae (SLSNe) at high redshifts, using the observationally-calibrated star formation rate density and supernova occurrence rate. We show that a 100 deg 2 survey with the limiting magnitude of 26 mag in near-infrared wavelengths will be able to discover about 10 SLSNe at z > 10. If the survey is extended to 200 deg 2 with 27 mag depth, about 10 SLSNe can be discovered at z > 15. We emphasize that the observations at � 3 �m are crucial to detect and select SLSNe at z > 10. Our simulations are also applied to the planned survey with Euclid, WFIRST, and WISH. These surveys will be able to detect about 1000, 400, and 3000 SLSNe up to z � 5, 7, and 12, respectively. We conclude that detection of SLSNe at z > 10 is in fact achievable in the near future.
54 citations
TL;DR: In this article, a spectrum covering optical through near-infrared (NIR) light of the luminous Type IIn supernova 2010jl around one and a half years after the explosion is presented.
Abstract: Supernovae (SNe) have been proposed to be the main production sites of dust grains in the universe. However, our knowledge of their importance to dust production is limited by observationally poor constraints on the nature and amount of dust particles produced by individual SNe. In this paper, we present a spectrum covering optical through near-Infrared (NIR) light of the luminous Type IIn supernova 2010jl around one and a half years after the explosion. This unique data set reveals multiple signatures of newly formed dust particles. The NIR portion of the spectrum provides a rare example where thermal emission from newly formed hot dust grains is clearly detected. We determine the main population of the dust species to be carbon grains at a temperature of ~1350-1450 K at this epoch. The mass of the dust grains is derived to be ~(7.5-8.5) × 10–4 M ☉. Hydrogen emission lines show wavelength-dependent absorption, which provides a good estimate of the typical size of the newly formed dust grains ( 0.1 μm, and most likely 0.01 μm). We believe the dust grains were formed in a dense cooling shell as a result of a strong SN-circumstellar media (CSM) interaction. The dust grains occupy ~10% of the emitting volume, suggesting an inhomogeneous, clumpy structure. The average CSM density must be 3 × 107 cm–3, corresponding to a mass loss rate of 0.02 M ☉ yr–1 (for a mass loss wind velocity of ~100 km s–1). This strongly supports a scenario in which SN 2010jl and probably other luminous SNe IIn are powered by strong interactions within very dense CSM, perhaps created by Luminous-Blue-Variable-like eruptions within the last century before the explosion.
45 citations
TL;DR: In this article, the effects of the recombination and the bolometric correction on light curves of shocked shells were considered and the results showed that the effect of recombination on the light curve was significant and the analytical model should be compared to the single band light curve instead of a single band LC.
Abstract: We numerically investigate light curves (LCs) of shocked circumstellar shells which are suggested to reproduce the observed LC of superluminous SN 2006gy analytically. In the previous analytical model, the effects of the recombination and the bolometric correction on LCs are not taken into account. To see the effects, we perform numerical radiation hydrodynamic calculations of shocked shells by using STELLA, which can numerically treat multigroup radiation transfer with realistic opacities. We show that the effects of the recombination and the bolometric correction are significant and the analytical model should be compare to the bolometric LC instead of a single band LC. We find that shocked circumstellar shells have a rapid LC decline initially because of the adiabatic expansion rather than the luminosity increase and the shocked shells fail to explain the LC properties of SN 2006gy. However, our synthetic LCs are qualitatively similar to those of superluminous SN 2003ma and SN 1988Z and they may be related to shocked circumstellar shells.
36 citations
TL;DR: In this paper, the authors present a study of SN?2009js in NGC?918, which is the first subluminous SN?IIP to be studied in the mid-infrared.
Abstract: We present a study of SN?2009js in NGC?918. Multi-band Kanata optical photometry covering the first ~120?days shows the source to be a Type?IIP?SN. Reddening is dominated by that due to our Galaxy. One-year-post-explosion photometry with the New Technology Telescope and a Subaru optical spectrum 16?days post-discovery both imply a good match with the well-studied subluminous SN?2005cs. The plateau-phase luminosity of SN?2009js and its plateau duration are more similar to the intermediate luminosity IIP?SN?2008in. Thus, SN?2009js shares characteristics with both subluminous and intermediate luminosity supernovae (SNe). Its radioactive tail luminosity lies between SN?2005cs and SN?2008in, whereas its quasi-bolometric luminosity decline from peak to plateau (quantified by a newly defined parameter ?log, which measures adiabatic cooling following shock breakout) is much smaller than both the others'. We estimate the ejected mass of 56Ni to be low (~0.007 M ?). The SN explosion energy appears to have been small, similar to that of SN?2005cs. SN?2009js is the first subluminous SN?IIP to be studied in the mid-infrared. It was serendipitously caught by Spitzer at very early times. In addition, it was detected by WISE 105?days later with a significant 4.6 ?m flux excess above the photosphere. The infrared excess luminosity relative to the photosphere is clearly smaller than that of SN?2004dj, which has been extensively studied in the mid-infrared. The excess may be tentatively assigned to heated dust with mass ~3 ? 10?5 M ?, or to CO fundamental emission as a precursor to dust formation.
27 citations
TL;DR: In this article, the link between luminous blue variables (LBVs) as SN progenitors and the appearance of episodic light curve modulations in the radio light curves of the SN event was investigated.
Abstract: Context. Ideally, one would like to know which type of core-collapse supernovae (SNe) is produced by different progenitors and what channels of stellar evolution lead to these progenitors. These links have to be very well known to use the observed frequency of different types of SN events for probing the star formation rate and massive star evolution in different types of galaxies. Aims. We investigate the link between luminous blue variables (LBVs) as SN progenitors and the appearance of episodic light curve modulations in the radio light curves of the SN event. Methods. We use the 20 Mand 25 Mmodels with rotation at solar metallicity, which are part of an extended grid of stellar models computed by the Geneva team. At their pre-SN stage, these two models have recently been shown to have spectra similar to those of LBV stars, and they possibly explode as Type IIb SNe. Based on the wind properties before the explosion, we derive the density structure of their circumstellar medium. This structure is used as input for computing the SN radio light curve. Results. We find that the 20 Mmodel shows radio light curves with episodic luminosity modulations similar to those observed in some Type IIb SNe. This occurs because the evolution of the 20 Mmodel terminates in a region of the HR diagram where radiative stellar winds present strong density variations, caused by the bistability limit. Ending its evolution in a zone of the HR diagram where no change of the mass-loss rates is expected, the 25 Mmodel presents no such modulations in its radio SN light curve. Conclusions. Our results reinforce the link between SN progenitors and LBV stars. We also confirm the existence of a physical mechanism for a single star to have episodic radio light curve modulations. In the case of the 25 Mprogenitors, we do not obtain modulations in the radio light curve, but our models may miss some outbursting behavior in the late stages of massive stars.
TL;DR: A fluorogenic NAD(P)(+) detection method using 2-acetylbenzofuran was successfully applied to the detection of P450 substrates in the microtiter-plate format.
TL;DR: In this article, the authors show that the spectra of PS1-10afx are well fit by normal Type Ia supernova (SNIa) templates and the multi-band colors and light-curve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z=1.3883.
Abstract: Recently, Chornock and co-workers announced the Pan-STARRS discovery of a transient source reaching an apparent peak luminosity of ~4x10^44 erg s^-1. We show that the spectra of this transient source are well fit by normal Type Ia supernova (SNIa) templates. The multi-band colors and light-curve shapes are also consistent with normal SNeIa at the spectroscopically determined redshift of z=1.3883; however, the observed flux is a constant factor of ~30 times too bright in each band over time as compared to the templates. At minimum, this shows that the peak luminosities inferred from the light-curve widths of some SNeIa will deviate significantly from the established, empirical relation used by cosmologists. We argue on physical grounds that the observed fluxes do not reflect an intrinsically luminous SNIa, but rather PS1-10afx is a normal SNIa whose flux has been magnified by an external source. The only known astrophysical source capable of such magnification is a gravitational lens. Given the lack of obvious lens candidates, such as galaxy clusters, in the vicinity, we further argue that the lens is a supermassive black hole or a comparatively low-mass dark matter halo. In this case, the lens continues to magnify the underlying host galaxy light. If confirmed, this discovery could impact a broad range of topics including cosmology, gamma-ray bursts, and dark matter halos.
TL;DR: In this paper, the origin of slowly rotating, non-evolved, nitrogen rich stars is discussed and it is shown that these stars may originate from initially fast rotating stars whose surface has been braked down.
Abstract: We discuss four questions dealing with massive star evolution. The first one is about the origin of slowly rotating, non-evolved, nitrogen rich stars. We propose that these stars may originate from initially fast rotating stars whose surface has been braked down. The second question is about the evolutionary status of α-Cygni variables. According to their pulsation properties, these stars should be post red supergiant stars. However, some stars at least present surface abundances indicating that they should be pre red supergiant stars. How to reconcile these two contradictory requirements? The third one concerns the various supernova types which are the end point of the evolution of stars with initial masses between 18 and 30 M ⊙ , i.e. the most massive stars which go through a red supergiant phase during their lifetime. Do they produce types IIP, IIL, IIn, IIb or Ib supernovae or do they end without producing any SN event? Finally, we shall discuss reasons why so few progenitors of type Ibc supernovae have yet been detected?
TL;DR: In this article, the authors investigated the link between LBV as SN progenitors and the appearance of episodic radio light curve modulations of the SN event and found that the 20Msun model shows radio light curves with episodic luminosity modulations, similar to those observed in some Type IIb SNe.
Abstract: Ideally, one would like to know which type of core-collapse SNe is produced by different progenitors and the channels of stellar evolution leading to these progenitors. These links have to be very well known to use the observed frequency of different types of SN events for probing the star formation rate and massive star evolution in different types of galaxies. We investigate the link between LBV as SN progenitors and the appearance of episodic radio light curve modulations of the SN event. We use the 20Msun and 25Msun models with rotation at solar metallicity, part of an extended grid of stellar models computed by the Geneva team. At their pre-SN stage, these two models have recently been shown to have spectra similar to those of LBV stars and possibly explode as Type IIb SNe. Based on the wind properties before the explosion, we derive the density structure of their circumstellar medium. This structure is used as input for computing the SN radio light curve. We find that the 20Msun model shows radio light curves with episodic luminosity modulations, similar to those observed in some Type IIb SNe. This occurs because the evolution of the 20Msun model terminates in a region of the HR diagram where radiative stellar winds present strong density variations, caused by the bistability limit. The 25Msun model, ending its evolution in a zone of the HR diagram where no change of the mass-loss rates is expected, presents no such modulations in its radio SN light curve. Our results reinforce the link between SN progenitors and LBV stars. We also confirm the existence of a physical mechanism for a single star to have episodic radio light curve modulations. In the case of the 25Msun progenitors, we do not obtain modulations in the radio light curve, but our models may miss some outbursting behavior in the late stages of massive stars.
01 Jan 2013
TL;DR: In this paper, a review of the emission processes within the supernova (SN) ejecta is presented, and the application of the theory to observational data is presented. But it is not shown how to obtain a complete view of the ejecta.
Abstract: Abstract We review emission processes within the supernova (SN) ejecta. Examples of the application of the theory to observational data are presented. The emission processes and thermal condition within the SN ejecta change as a function of time, and multi-epoch observations are important to obtain comprehensive views. Through the analyses, we can constrain the progenitor radius, compositions as a function of depth, ejecta properties, explosion asymmetry and so on. Multi-frequency follow-up is also important, including radio synchrotron emissions and the inverse Compton effect, γ-ray emissions from radioactive decay of newly synthesized materials. The optical data are essential to make the best use of the multi-frequency data.
TL;DR: In this article, the origin of slowly rotating, non-evolved, nitrogen rich stars is discussed and it is shown that these stars may originate from initially fast rotating stars whose surface has been braked down.
Abstract: We discuss four questions dealing with massive star evolution. The first one is about the origin of slowly rotating, non-evolved, nitrogen rich stars. We propose that these stars may originate from initially fast rotating stars whose surface has been braked down. The second question is about the evolutionary status of alpha-Cygni variables. According to their pulsation properties, these stars should be post red supergiant stars. However, some stars at least present surface abundances indicating that they should be pre red supergiant stars. How to reconcile these two contradictory requirements? The third one concerns the various supernova types which are the end point of the evolution of stars with initial masses between 18 and 30 Msun, i.e. the most massive stars which go through a red supergiant phase during their lifetime. Do they produce types IIP, IIL, IIn, IIb or Ib supernovae or do they end without producing any SN event? Finally, we shall discuss reasons why so few progenitors of type Ibc supernovae have yet been detected?
01 Jan 2013
TL;DR: In this article, the authors performed numerical simulations of collisions of SN ejecta and dense CSM by using one-dimensional radiation hydrodynamics code STELLA and obtained light curves (LCs) resulting from the collision.
Abstract: Origins of superluminous supernovae (SLSNe) discovered by recent SN surveys are still not known well. One idea to explain the huge luminosity is the collision of dense CSM and SN ejecta. If SN ejecta is surrounded by dense CSM, the kinetic energy of SN ejecta is efficiently converted to radiation energy, making them very bright. To see how well this idea works quantitatively, we performed numerical simulations of collisions of SN ejecta and dense CSM by using one-dimensional radiation hydrodynamics code STELLA and obtained light curves (LCs) resulting from the collision. First, we show the results of our LC modeling of SLSN 2006gy. We find that physical parameters of dense CSM estimated by using the idea of shock breakout in dense CSM (e.g., Chevalier & Irwin 2011, Moriya & Tominaga 2012) can explain the LC properties of SN 2006gy well. The dense CSM's radius is about 1016 cm and its mass about 15 M⊙. It should be ejected within a few decades before the explosion of the progenitor. We also discuss how LCs change with different CSM and SN ejecta properties and origins of the diversity of H-rich SLSNe. This can potentially be a probe to see diversities in mass-loss properties of the progenitors. Finally, we also discuss a possible signature of SN ejecta-CSM interaction which can be found in H-poor SLSN.
TL;DR: In this paper, a spectrum covering optical through near-infrared (NIR) light of the luminous Type IIn supernova (SN IIn) 2010jl around one and half years after the explosion is presented.
Abstract: Supernovae (SNe) have been proposed to be the main production sites of dust grains in the Universe. Our knowledge on their importance to dust production is, however, limited by observationally poor constraints on the nature and amount of dust particles produced by individual SNe. In this paper, we present a spectrum covering optical through near-Infrared (NIR) light of the luminous Type IIn supernova (SN IIn) 2010jl around one and half years after the explosion. This unique data set reveals multiple signatures of newly formed dust particles. The NIR portion of the spectrum provides a rare example where thermal emission from newly formed hot dust grains is clearly detected. We determine the main population of the dust species to be carbon grains at a temperature of ~1,350 - 1,450K at this epoch. The mass of the dust grains is derived to be ~(7.5 - 8.5) x 10^{-4} Msun. Hydrogen emission lines show wavelength-dependent absorption, which provides a good estimate on the typical size of the newly formed dust grains (~0.1 micron, and most likely ~3 x 10^{7} cm^{-3}, corresponding to a mass loss rate of >~0.02 Msun yr^{-1} (for a mass loss wind velocity of ~100 km s^{-1}). This strongly supports a scenario that SN 2010jl and probably other luminous SNe IIn are powered by strong interactions within very dense CSM, perhaps created by Luminous Blue Variable (LBV)-like eruptions within the last century before the explosion.
TL;DR: In this paper, the authors present a study of SN 2009js in NGC 918, which is the first subluminous SN IIP to be studied in the mid-infrared.
Abstract: We present a study of SN 2009js in NGC 918. Multi-band Kanata optical photometry covering the first ~120 days show the source to be a Type IIP SN. Reddening is dominated by that due to our Galaxy. One-year-post-explosion photometry with the NTT, and a Subaru optical spectrum 16 days post-discovery, both imply a good match with the well-studied subluminous SN 2005cs. The plateau phase luminosity of SN 2009js and its plateau duration are more similar to the intermediate luminosity IIP SN 2008in. Thus, SN 2009js shares characteristics with both subluminous and intermediate luminosity SNe. Its radioactive tail luminosity lies between SN 2005cs and SN 2008in, whereas its quasi-bolometric luminosity decline from peak to plateau (quantified by a newly-defined parameter Delta[logL] measuring adiabatic cooling following shock breakout) is much smaller than both the others. We estimate the ejected mass of 56Ni to be low (~0.007 Msun). The SN explosion energy appears to have been small, similar to SN 2005cs. SN 2009js is the first subluminous SN IIP to be studied in the mid-infrared. It was serendipitously caught by Spitzer at very early times. In addition, it was detected by WISE 105 days later with a significant 4.6 micron flux excess above the photosphere. The infrared excess luminosity relative to the photosphere is clearly smaller than that of SN 2004dj extensively studied in the mid-infrared. The excess may be tentatively assigned to heated dust with mass ~3e-5 Msun, or to CO fundamental emission as a precursor to dust formation.