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— Multi-wavelength V838 Mon images. Column 1: MIPS 24, 70, and 160 μ m images (top to bottom); Column 2: PSF subtracted images (no point source detected at 160 μ m, see text); Column 3: HST F814W image convolved to the MIPS resolution at 24, 70, and 160 μ m images (top to bottom) after removal of field stars in the HST image. MIPS beam sizes are indicated by the white circles with FWHM of 6 ′′ , 18 ′′ , and 40 ′′ . All images are displayed in a field of view of 160 ′′ by 160 ′′ , with N up and E toward the left, and in false-color
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We present Spitzer observations of the unusual variable V838 Monocerotis. Extended emission is detected around the object at 24, 70 and 160um. The extended infrared emission is strongly correlated spatially with the HST optical light echo images taken at a similar epoch. We attribute this diffuse nebulosity to be from an infrared light echo caused...
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... eruption of V838 Monocerotis (V838 Mon) in Jan- uary 6, 2002 has introduced a seemingly new kind of object in the realm of cataclysmic variables. It was detected in eruption by Brown (2002) with a peak outburst am- plitude of V max = 10 which was followed by two more outbursts – within the next two months – reaching 6.7 and 7 magnitudes respectively. V838 Mon also showed fast cooling, on a timescale of a few months, to a cool, late M spectral type or beyond (Evans et al. 2003). The multi- peaked outbursts in the object and the decrease of its effective temperature with time suggested that the object was different from a classical nova or other known classes of eruptive variables (Munari et al. 2002; Kimeswenger et al. 2002). An expanding light-echo was also seen around the star (Henden et al. 2002) whose expansion and accompanying morphological changes are strikingly illustrated by HST (Bond et al. 2003) and other images (Crause et al. 2005). Distance estimates to the object, converging to a large value in the range of 7-10 kpc, have been made based on varied approaches such as the rate of the expanding light echo (e.g., Tylenda 2004; Crause et al. 2005), and the detection of SiO maser emission from the source (Deguchi et al. 2005). Con- siderable near-infrared studies of the source have been done yielding spectra showing an oxygen rich atmosphere with prominent molecular features of CO, AlO, SiO, TiO and water (Lynch et al. 2004; Evans et al. 2003; Banerjee & Ashok 2002; Rushton et al. 2005). Though not firmly established, similarities in outburst properties between V838 Mon and two other potential analogs viz. V4332 Sgr and M31-RV, suggest that they could be uni- fied into a new class of eruptive variables. While the cause for the intriguing outbursts in such objects is yet to be securely established, various mechanisms have been proposed viz. the merger between main sequence stars (Soker & Tylenda 2003); the capture of multiple plane- tary companions (Retter & Marom 2003) or a late flash in a born-again AGB star (Lawlor 2005). Aspects relat- ing to the spectral type of the progenitor and whether it is a single or binary star have also been the subject of investigations (Munari et al. 2005; Tylenda et al. 2005). Here, we present our results on V838 Mon from GO Cycle 1 observations of the Spitzer Space Telescope ( Spitzer ). The highlight of the Spitzer observations is the striking infrared echo seen around V838 Mon in the mid- and far-IR images. While optical light echoes around novae or supernovae are rare but not unknown, an infrared “echo” is a rare complementary phenomenon – we are only aware of one other instance of a resolved infrared light echo, Cas A (Krause et al. 2005). When photons from the illuminating source interact with the dust grains of the echo material, they can either be absorbed or scattered according to the albedo of the grain. Pho- tons scattered into the line of sight result in an optical light echo, a direct “image” of the impinging radiation. On the other hand, IR “echoes” result from the absorption of the impinging radiation; the thermalized energy of the absorbed photons is re-emitted in the IR. Our observations are presented in § 2. Details of the nature of the IR emission are discussed in § 3. In § 4, the important question regarding the origin of the light echo material around V838 Mon is discussed. V838 Mon was imaged with the Multiband Imaging Photometer for Spitzer (MIPS; Rieke et al. 2004) at 24, 70 and 160 μ m in 2004 and 2005. The log of the observations is given in Table 1. The MIPS data were reduced using the Data Analy- sis Tool (DAT; Gordon et al. 2005). Images at 24, 70, and 160 μ m are shown in the first column of Figure 1. While at 24 μ m, V838 Mon appears as a bright point source (hard saturation in the core), extended nebulosity offset from the central star is readily apparent at ...
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... 160 μ m. Detailed comparison of the 24 μ m radial profiles between the target and an observed standard star indicates that the profiles matched very well between the first bright and dark Airy rings, suggesting most of the flux at the central region is from an unresolved source, and the extended nebulosity contributes very little flux at the core. To correct the saturation in the 24 μ m image, an observed point spread function (PSF) was scaled to match the brightness of the first bright Airy ring. The saturated core of V838 Mon was then replaced with the scaled PSF. Total fluxes observed through 80 ′′ apertures are reported in column 2 of Table 2. To separate the extended emission from the unresolved point source, PSF subtraction was performed on the 24 and 70 μ m images (at 160 μ m, there is no discernible unresolved central source). The flux density of the central source estimated from the subtracted PSF is reported in column 3 of Table 2. The PSF subtracted images are presented in column 2 of Figure 1. Extended emission is clearly evident at 24 μ m in the PSF subtracted images, especially a bright extension to the south of V838 Mon. The total diffuse flux observed toward V838 Mon, obtained by subtracting the unresolved point source flux from that measured in the 80 ′′ aperture, is given in column 4 of Table 2. In order to compare our infrared images with the optical light echo, we have also obtained archival HST ACS images of V838 Mon (Hubble Heritage, GO/DD 10392). The data were obtained with the ACS/WFC using the F435W, F606W, and F814W filters and were completed on 23 Oct 2004, within days of our 24 and 160 μ m observations and a few months of our 70 μ m observations. The F814W image convolved with the MIPS beams is shown in column 3 of Figure 1 for comparison. A three color composite image was constructed using all three HST filters and is presented in Figure 2 with our 24, 70, and 160 μ m contours superposed. The 24 − 160 μ m spectral energy distribution (SED) of the extended ...
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... 160 μ m. Detailed comparison of the 24 μ m radial profiles between the target and an observed standard star indicates that the profiles matched very well between the first bright and dark Airy rings, suggesting most of the flux at the central region is from an unresolved source, and the extended nebulosity contributes very little flux at the core. To correct the saturation in the 24 μ m image, an observed point spread function (PSF) was scaled to match the brightness of the first bright Airy ring. The saturated core of V838 Mon was then replaced with the scaled PSF. Total fluxes observed through 80 ′′ apertures are reported in column 2 of Table 2. To separate the extended emission from the unresolved point source, PSF subtraction was performed on the 24 and 70 μ m images (at 160 μ m, there is no discernible unresolved central source). The flux density of the central source estimated from the subtracted PSF is reported in column 3 of Table 2. The PSF subtracted images are presented in column 2 of Figure 1. Extended emission is clearly evident at 24 μ m in the PSF subtracted images, especially a bright extension to the south of V838 Mon. The total diffuse flux observed toward V838 Mon, obtained by subtracting the unresolved point source flux from that measured in the 80 ′′ aperture, is given in column 4 of Table 2. In order to compare our infrared images with the optical light echo, we have also obtained archival HST ACS images of V838 Mon (Hubble Heritage, GO/DD 10392). The data were obtained with the ACS/WFC using the F435W, F606W, and F814W filters and were completed on 23 Oct 2004, within days of our 24 and 160 μ m observations and a few months of our 70 μ m observations. The F814W image convolved with the MIPS beams is shown in column 3 of Figure 1 for comparison. A three color composite image was constructed using all three HST filters and is presented in Figure 2 with our 24, 70, and 160 μ m contours superposed. The 24 − 160 μ m spectral energy distribution (SED) of the extended ...
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... Shortly after its eruption in 2002 (Brown et al. 2002), a light echo-due to reflection of the eruption off circumstellar dust-became very prominent (Bond et al. 2003). The echo was also prominent in Spitzer (+MIPS; Banerjee et al. 2006) and Herschel (Exter et al. 2016) imagery at λ 70 μm. V838 Mon is 6.2 kpc distant, a value tightly constrained from polarized light echo studies (Sparks et al. 2008). ...
Luminous Red Variables are most likely eruptions that are the outcome of stellar mergers. V838 Mon is one of the best-studied members of this class, representing an archetype for stellar mergers resulting from B-type stars. As result of the merger event, “nova-like” eruptions occur driving mass loss from the system. As the gas cools considerable circumstellar dust is formed. V838 Mon erupted in 2002 and is undergoing very dynamic changes in its dust composition, geometry, and infrared luminosity providing a real-time laboratory to validate mineralogical condensation sequences in stellar mergers and evolutionary scenarios. We discuss recent NASA Stratospheric Observatory for Infrared Astronomy 5–38 μ m observations combined with archival NASA Spitzer spectra that document the temporal evolution of the freshly formed (within the last ≲20 yr) circumstellar material in the environs of V838 Mon. Changes in the 10 μ m spectral region are strong evidence that we are witnessing a classical dust condensation sequence expected to occur in oxygen-rich environments where alumina formation is followed by that of silicates at the temperature cools.
... Both objects underwent initial large-amplitude novalike outbursts but it was soon realized that they were different from classical novae or other known classes of CVs (e.g., Munari et al. 2002). Worth mentioning specifically is the haloed status achieved by V838 Mon by virtue of the striking light echo that adorned it (Bond et al. 2003;Banerjee et al. 2006). A general consensus exists today that they belong to a new class of eruptive variables called intermediate luminosity red transients (ILRTs; Bond et al. 2011). ...
We describe a search for the A-X infrared bands of AlO with a view to better
understand the characteristics of this radical. These bands are infrequently
encountered in astronomical sources but surprisingly were very prominent in the
spectra of two well-known, nova-like variables (V838 Mon and V4332 Sgr) thereby
motivating us to explore the physical conditions necessary for their
excitation. In this study, we present the detection of A-X bands in the spectra
of 13 out of 17 stars, selected on the basis of their J-K colors as potential
candidates for detection of these bands. The majority of the AlO detections are
in AGB stars viz. 9 OH/IR stars, 2 Mira variables and 2 bright infrared
sources. Our study shows that the A-X bands are fairly prevalent in sources
with low temperature and O-rich environments. Interesting variation in strength
of the AlO bands in one of the sources (IRAS 18530+0817) is reported and the
cause for this is examined. Possible applications of the present study are
discussed in terms of the role of AlO in alumina dust formation, the scope for
estimating the radioactive $^{26}$Al content in AGB stars from the A-X bands,
and providing possible targets for further mm/radio studies of AlO which has
recently been discovered at millimeter wavelengths.
We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at −13 to −15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490−2011OT1, M 101−2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H α is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (∼6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H α is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.
Herschel FIR imaging and spectroscopy were taken at several epochs to probe the central point source and the extended environment of V838 Mon. PACS and SPIRE maps were used to obtain photometry of the near and far dust around V838 Mon. Fitting reveals 0.5-0.6 solar masses of ~19K dust in the environs (~2.7pc) surrounding the star. The surface-integrated infrared flux (signifying the thermal light echo) and derived dust properties do not vary significantly between the epochs. We also fit the SED of the point source. As the peak of the SED lies outside the Herschel spectral range, it is only by incorporating data from other observatories and epochs that we can perform useful fitting; with this we explicitly assume no evolution of the point source between the epochs. We find warm dust with a temperature of ~300K distributed over a radius of 150-200AU. PACS and SPIRE spectra were also used to detect emission lines from the extended environment around the star. We fit the far-infrared lines of CO arising from the point source, from an extended environment around V838 Mon. Assuming a model of a spherical shell for this gas, we find that the CO appears to arise from two temperature zones: a cold zone (Tkin ~18K) that could be associated with the ISM or possibly with a cold layer in the outermost part of the shell, and a warm (Tkin ~400K) zone that is associated with the extended environment of V838 Mon within a region of radius of ~210AU. The SiO lines arise from a warm/hot zone. We did not fit the lines of H2O as they are far more dependent on the model assumed.
Aims. V838 Monocerotis erupted in 2002, brightened in a series of outbursts,
and eventually developed a spectacular light echo. A very red star emerged a
few months after the outburst. The whole event has been interpreted as the
result of a merger. Methods. We obtained near-IR and mid-IR interferometric
observations of V838 Mon with the AMBER and MIDI recombiners located at the
Very Large Telescope Interferometer (VLTI) array. The MIDI two-beam
observations were obtained with the 8m Unit Telescopes between October 2011 and
February 2012. The AMBER three-beam observations were obtained with the compact
array (Bâ¤35m) in April 2013 and the long array (Bâ¤140m) in May 2014, using the
1.8m Auxiliary Telescopes. Results. A significant new result is the detection
of a compact structure around V838 Mon, as seen from MIDI data. The extension
of the structure increases from a FWHM of 25 mas at 8 {\mu}m to 70 mas at 13
{\mu}m. At the adopted distance of D = 6.1 $\pm$ 0.6 kpc, the dust is
distributed from about 150 to 400 AU around V838 Mon. The MIDI visibilities
reveal a flattened structure whose aspect ratio increases with wavelength. The
major axis is roughly oriented around a position angle of âÂÂ10â¦, which aligns
with previous polarimetric studies reported in the literature. This flattening
can be interpreted as a relic of the 2002 eruption or by the influence of the
currently embedded B3V companion. The AMBER data provide a new diameter for the
pseudo-photosphere, which shows that its diameter has decreased by about 40% in
10yrs, reaching a radius Râ = 750 $\pm$ 200 Râ (3.5 $\pm$ 1.0 AU). Conclusions.
After the 2002 eruption, interpreted as the merging of two stars, it seems that
the resulting source is relaxing to a normal state. The nearby environment
exhibits an equatorial over-density of dust up to several hundreds of AU.
BT2 is the most accurate and complete synthetic water line list in
existence; it includes over 505 million transitions. BT2 spectra
generated at various temperatures and column densities were fitted to
observed H band spectra of V838 Mon recorded on 5 dates between 20 Nov.
2002 and 25 Dec. 2004. Five absorption features in the observed spectra
were identified as being due to water. With one exception, where there
was a single strong water line, all of the featues were blends of water
lines. 17 individual water lines were assigned and the rotational
temperatures and H_2O column densities of the circumstellar ejected
envelope were determined for each of the five dates.
A J-band polarimetric image was taken for V838 Monocerotis with the imaging polarimeter SIRPOL on the IRSF 1.4-m telescope at the South African Astronomical Observatory. A diffuse nebulosity is seen in the north-east and the south-west directions of the central star in the PI image. The polarization vectors reveal a circular feature indicating that the nebulous light is the scattered light from the central star. The polarization degree reaches up to 40-percent in the outer part of the nebula.
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in the hope that it might keep us going another few hundred thousand years.
Aims:We investigate the structure of a field around the position of V838 Mon as seen in the lowest CO rotational transitions. We also measure and analyse emission in the same lines at the position of V838 Mon. Methods: Observations have primarily been done in the 12CO J = 2-->1 and J = 3-->2 lines using the KOSMA telescope. A field of 3.4 squared degrees has been mapped in the on-the-fly mode in these transitions. Longer integration spectra in the on-off mode have been obtained to study the emission at the position of V838 Mon. Selected positions in the field have also been observed in the 12CO J = 1-->0 transition using the Delingha telescope. Results: In the observed field we have identified many molecular clouds. They can be divided into two groups from the point of view of their observed radial velocities. One, having V_LSR in the range 18-32 km s-1, can be identified with the Perseus Galactic arm. The other one, having V_LSR between 44-57 km s-1, probably belongs to the Norma-Cygnus arm. The radial velocity of V838 Mon is within the second range but the object does not seem to be related to any of the observed clouds. We did not find any molecular buble of a 1° dimension around the position of V838 Mon claimed in van Loon et al. An emission has been detected at the position of the object in the 12CO J = 2 -->1 and J = 3-->2 transitions. The emission is very narrow (FWHM ~= 1.2 km s-1) and at V_LSR = 53.3 km s-1. Our analysis of the data suggests that the emission is probably extended. Appendix is only available in electronic form at http://www.aanda.org
Context: V838 Mon erupted at the beginning of 2002, becoming an extremely luminous star with L = 106 L&sun;. The outburst was followed by a spectacular light echo that revealed that the star is immersed in a diffuse and dusty medium, plausibly interstellar in nature. Low angular-resolution observations of the star and its closest vicinity in the lowest CO rotational transitions revealed a molecular emission from the direction of V838 Mon. The origin of this CO emission has not been estalished. Aims: The main aim of this paper is to better constrain the nature of the CO emission. In particular, we investigate the idea that the molecular emission originates in the material responsible for the optical light echo. Methods: We performed observations of 13 positions within the light echo in the two lowest rotational transitions of 12CO using the IRAM 30 m telescope. Results: Emission in CO J = 1-0 and J = 2-1 was detected in three positions. In three other positions only weak J = 1-0 lines were found. The lines appear at two different velocities VLSR = 53.3 km s-1 and V_LSR = 48.5 km s-1, and both components are very narrow with FWHM ≈ 1 km s-1. Conclusions: The molecular emission from the direction of V838 Mon is extended and has a complex distribution. We identify the emission as arising from diffuse interstellar clouds. A rough estimate of the mass of the molecular matter in those regions gives a few tens of solar masses. The radial velocity of the emission at 53.3 km s-1 suggests that the CO-bearing gas and the echoing dust are collocated in the same interstellar cloud. Based on observations carried out with the IRAM 30-meter telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). Appendix A is only available in electronic form at http://www.aanda.org
