v838 monocerotis distance from earth

Figure 7. Sie ist etwa 6,1 Kiloparsec (20.000 Lichtjahre) von der Erde entfernt und besitzt eine scheinbare Helligkeit von 15,74 mag. © 2008. The star forms part of the shoulder of an imagined unicorn in the constellation Monoceros, 20,000 light-years away, and in January 2002, astronomers saw it blow up. 1992). However, Afşar & Bond (2007) have argued that this is an overestimate because the B star suffers extinction over and above that due to the foreground interstellar medium; this extra extinction would be due to the B star lying within (or behind) the dust ejected from V838 Mon during the 2002 outburst. To convert this electric-vector position angle in the detector frame to an astronomical position angle on the sky, θS (defined, as usual, with north at 0° and east at 90°), we used the formula, where θV3 is the position angle of the spacecraft V3 axis on the sky, available in ACS images as the FITS image-header keyword "PA_V3.". Sparks (1994, 1996) showed that polarimetric observations of a light echo may be used to derive a purely geometric distance to the source. If the dust did come from a previous outburst, it would cast doubt on the stellar-merger scenarios, which presumably would be one-time events.

Photometric coverage of its outburst, collected by Boschi & Munari (2004, their Table 5), was unfortunately fairly sparse, especially in the V band. S Mon is a barely-fifth magnitude (nominally 4.66) blue- white class O (O7) dwarf in the constellation Monoceros.

V838 Mon was brighter at maximum than all but the very fastest of classical novae (e.g., Downes & Duerbeck 2000, their Figure 17). William B. Sparks1, Howard E. Bond1, Misty Cracraft1, Zolt Levay1, Lisa A. Crause2, Michael A. Dopita3, Arne A. Henden4, Ulisse Munari5, Nino Panagia1,6,7, Sumner G. Starrfield8, Ben E. Sugerman9, R. Mark Wagner10, and Richard L. White1, Published 2008 January 16 • The primary problem is S Mon’s distance. Higher masses could do the job, but these are out of line with the combination of orbital solution and cluster distance. Theoretically, White (1979) used Mie theory to calculate the scattering properties of the Mathis et al. The use of light-echo polarimetry to obtain geometric distances of supernovae (SNe) was proposed by Sparks (1994). a Position angle of the electric vector measured counter-clockwise from the spacecraft V3 axis. The appearance of a light echo is governed by the time-dependent brightness of the illuminating source, the density and scattering properties of the dust, and the distance to the star. Linear polarization degree plotted as a function of scattering angle, as derived for the 2002 December data and assumed distances of 8 kpc (inner curve), 6 kpc (middle noisy curve), and 4 kpc (outer curve). The apparent magnitude of V838 Mon at its maximum in early 2002 February was V = 6.77 (see Figure 5).

The American Astronomical Society.

The data were first processed through the standard Space Telescope Science Institute (STScI) calibration pipeline in order to de-bias and flat-field the individual images. x�b``�f``_���� _� ̀ ��@Q�*�G� L It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics. 2002), while cometary dust is found empirically to have a maximum polarization of about 30% at about 90° (Moreno et al.

(2002).

The uncertainty is higher here since the errors on both individual measurements combine quadratically. For reference we also show the Rayleigh phase function as a smooth curve in Figure 12. 0000007958 00000 n While the intensity distribution of an echo can be highly complex since it depends largely on the density of the scattering medium, the linear-polarization distribution should be simple, smooth, and dependent only on the projected linear radius from the star and the time since the outburst.

Thus the total emitted flux is equivalent to the Vmax brightness shining for 38 days.


Figure 7 shows a color rendition of the 2002 December 17 observations prepared by one of us (Z.L.) Nothing lasts forever, but in the universe, nothing is ever really gone, either. One or both are rotating rather quickly, at least 63 kilometers per second. (2003), but are plotted here as stellar magnitudes rather than on a linear flux scale. Mergers have the advantage of possibly occurring in both young and old populations. Second, the presence of a substantial number of stars in the FOV complicates the analysis. To estimate the distance geometrically, we return to the basic assumption that polarization maximizes at a scattering angle of 90°. 0000006135 00000 n 0000008936 00000 n

The amount by which the simulated data were smoothed (determined empirically) was assumed to apply to the drizzled error image, and hence the estimated uncertainty on each pixel intensity was determined. The observer is located on the +z axis, V838 Mon lies at the (0,0) origin, and the x and z distances from the star are in units of ACS pixels (0'05) for an adopted distance of 6.1 kpc.
(V838 Mon M31 RV V4332 Sgr) 0000007818 00000 n

As discussed in Section 5.3, we adopted θmax = 90° ± 5°.

The spectacular light echo of V838 Mon thus offers a unique opportunity to test this technique, and also to contribute to a physical understanding of this extraordinary object by determining its distance and luminosity. These issues do not affect our distance determination, and are thus beyond the scope of the present paper; see the recent conference proceedings for discussions of the origin of the dust (Corradi & Munari, eds., 2007).

The electric vectors are seen generally to be oriented perpendicular to the direction to the central star. The images illustrating polarization degree shown in Figure 2 are here masked to retain only regions free of stars and with linear polarization degree detected with S/N>10, as described in the text. At each epoch, the solid line marks light from the end of the outburst (shortest time delay), and the dashed line marks the beginning of the outburst (longest time delay). The echo phenomenon occurs when light from an eruptive variable is scattered by dust in its vicinity, reaching the Earth at progressively later times as the wave of illumination propagates outward. Following a careful reduction of polarimetric images of the light echo, obtained with the ACS onboard the HST, we confirmed the presence of an apparently expanding ring of highly polarized light surrounding V838 Mon. Division of the integrated Stokes Q function by the integrated intensity I yielded a model polarization degree, which was used for comparison with the data. The answer could be relevant to our plight.

For astronomical distances, this ellipsoid is well approximated by the paraboloid given by z = x2/2ct − ct/2, where x is the projected distance from the star in the plane of the sky, z is the distance from this plane along the line of sight (LOS) toward the Earth, c is the speed of light, and t is the time since the outburst. 0000020837 00000 n

The uncertainty in our final distance estimate is dominated by systematic errors, with the primarily source being the uncertainty in the scattering angle that produces maximum linear polarization.

In order to model the polarization distribution of the echo, we began by combining the light-curve data given in Section 4.1 and plotted in Figure 5 with the three-dimensional geometry described in Section 4.2 and illustrated in Figure 6, to produce a set of source functions. As a result, the death of V 838 Monocerotis is giving astronomers a rare look at the circumstances that gave it birth. These are two-dimensional functions (projected distance from the star and LOS distance), with rotational symmetry assumed for the third dimension.

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