20 February 2006
IAU Circular No.8673
RS OPHIUCHI
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R. K. Das, N. M. Ashok, and D. P. K. Banerjee, Physical
Research Laboratory, report that near-infrared JHK spectroscopy of
RS Oph during its current outburst (cf. IAUC 8671), obtained with
the Mt. Abu 1.2-m telescope (+ PRL Near Infrared NICMOS3
Imager/Spectrometer) on Feb. 16.99 UT, shows prominent H I
emission lines of Paschen_beta, Paschen_gamma, Brackett_gamma,
Brackett_10 through Brackett_19, He I at 1.0830 and 2.0581 microns,
and O I at 1.1288 microns.
CCD magnitudes by G. Sostero and E. Guido, Udine, Italy (via a
remotely operated 0.25-m reflector near Mayhill, NM): Feb. 13.490
UT, B = 5.90; 13.491, V = 5.00; 13.493, R_c = 4.40; 14.487, B =
6.25; 14.488, V = 5.47; 14.490, R_c = 4.40; 16.484, B = 6.99;
16.485, V = 6.23; 16.487, R_c = 5.04; 20.481, B = 8.03; 20.483, V =
7.23; 20.485, R_c = 5.05.
21 February 2006
IAU Circular No.8675
RS OPHIUCHI
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T. Iijima, Osservatorio Astrofisico, Asiago, writes that high-
dispersion spectra (resolution 16000; range 420-680 nm) of RS Oph
were taken with an echelle spectrograph mounted on the 1.82-m
reflector at the Mt. Ekar station of the Astronomical Observatory
of Padova on Feb. 18.2 and 19.2 UT. The spectra show broad
emission lines of H I, He I, Fe II multiplets 27, 37, 38, 42, 43,
48, 49, and 74, and some Ti II lines. The emission lines of He II
were not yet detected. The FWHM of H I and He I lines are about
1800 km/s, and those of the Fe II lines are roughly 800 km/s. Very
narrow emission components, whose widths are comparable to the
resolution limit of the spectrograph, are seen on the top of the
broad emission components. The narrow components are very weak for
H I and He I lines, while their heights are larger than those of
the broad components for several Fe II lines. The line of [N II]
575.5-nm shows only the narrow component.
M. F. Bode, Liverpool John Moores University; T. J. O'Brien
and R. J. Davis, University of Manchester; J. Osborne and K. L.
Page, University of Leicester; G. Schwarz, West Chester University;
S. Starrfield and J.-U. Ness, Arizona State University; J. Krautter,
University of Heidelberg; J. Drake, Smithsonian Astrophysical
Observatory; A. Evans, Keele University; and S. P. S. Eyres,
University of Central Lancashire, report that Swift XRT
observations of the latest outburst of RS Oph (IAUC 8671) show this
to be a very bright and rapidly evolving x-ray source: "The first
observations, obtained on Feb. 16.21 UT (3.38 days after reported
outburst), gave a total XRT countrate of 11.8 +/- 0.2 counts/s.
The x-ray spectrum could be well fitted with a strongly absorbed
high-temperature thermal bremsstrahlung model plus an Fe K line and
absorption edge: kT > 70 keV (90-percent confidence), E_line =
6.66 +/- 0.02 keV, E_edge = 7.18 +/- 0.09 keV, and N_H = (2.3 +/-
0.1) x 10**(22) cm**(-2). Observations on Feb. 17.89 show the
source to be around three times brighter in the XRT band, and the
spectrum shows clear evidence of line emission from other elements
as well as Fe. A preliminary solar abundance spectral fit requires
four temperature components plus an Fe K line and absorption edge.
In this fit, N_H = (1.7 +0.11/-0.22) x 10**(22) cm**(-2). We note
that these fits may not be unique and should be considered simply
empirical at this stage. Detailed hydrodynamic modelling is now in
progress. Observations and modelling of the previous outburst in
1985 (see, e.g., O'Brien et al. 1992, MNRAS 255, 683) suggest that
RS Oph will continue to evolve rapidly in the x-ray range over the
coming weeks. We also urge continued monitoring at other
wavelengths, in particular optical spectroscopy, for the next
several months. Swift observations are ongoing."
22 February 2006
IAU Circular No.8677
RS OPHIUCHI
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Corrigenda. M. Bode advises us that the observation times
given on IAUC 8675 (lines 9 and 14 of the second item, printed
version) should read Feb. 16.00 (or 3.17 days after the reported
optical outburst) and 17.86 UT.
24 February 2006
IAU Circular No.8678
RS OPHIUCHI
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S. P. S. Eyres, University of Central Lancashire; T. J.
O'Brien and T. W. B. Muxlow, University of Manchester; M. F. Bode,
Liverpool John Moores University; and A. Evans, Keele University,
report the detection of RS Oph in the radio. On Feb. 17.5 UT (4.7
days after the reported outburst; cf. IAUC 8671), Very Large Array
(VLA) observations show fluxes of 2.8 +/- 0.2 mJy at 21.1 cm, 15.2
+/- 0.2 mJy at 6.2 cm, 23.2 +/- 0.6 mJy at 2 cm, and 26.2 +/- 0.5
mJy at 1.3 cm. Observations with MERLIN show 5-cm fluxes of 31.2
+/- 0.9 mJy on Feb. 18 and 39.5 +/- 0.9 mJy on Feb. 20. This is
much brighter than anticipated at this stage when compared with
observations of the 1985 outburst (23 mJy on day 18 of outburst; cf.
Padin, Davis, and Bode 1985, Nature 315, 306). Further VLA, MERLIN,
VLBA, and EVN observations are being scheduled. All observers are
urged to secure spectroscopic and photometric observations of this
star over the next few days, weeks, and months.
1 March 2006
IAU Circular No.8681
RS OPHIUCHI
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Additional photometry by G. Sostero and E. Guido (cf. IAUC
8673): Feb. 21.48 UT, V = 7.36, B-V = +0.70; 22.48, 7.43, +0.66;
24.48, 7.70, +0.79; 25.48, 7.75, +0.65; 26.47, 7.76, +0.65; 27.48,
8.04, +0.62.
2 March 2006
IAU Circular No.8682
RS OPHIUCHI
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A. Evans, Keele University; T. Kerr, Joint Astronomy Centre;
Y. Matsuoka and Y. Tsuzuki, University of Tokyo; T. R. Geballe,
Gemini Observatory; R. D. Gehrz and C. E. Woodward, University of
Minnesota; M. F. Bode, Liverpool John Moores University; T. J.
O'Brien and R. J. Davis, University of Manchester; J. P. Osborne
and K. L. Page, University of Leicester; G. Schwarz, West Chester
University; S. Starrfield and J.-U. Ness, Arizona State University;
J. Krautter, University of Heidelberg; J. Drake, Smithsonian
Astrophysical Observatory; and S. P. S. Eyres, University of
Central Lancashire, report that a spectrum (range 880 nm-2.5
microns) was obtained with the 3.8-m U.K. Infrared Telescope (+
UIST) on Feb. 24.64 UT. The spectra show strong Paschen lines from
4-3 to 12-3, Brackett lines from 7-4 to 20-4, Pfund lines from 17-5
to 23-5, He I at 1.083, 2.058, and 2.112 microns, O I 3P-3D^0 at
1.128 microns (cf. IAUC 8673), and other lines that are tentatively
identified with O I, O II and C I. The FWHM of the resolved
Paschen_alpha line is 1130 +/- 50 km/s, but with wings extending to
3000 km/s.
IAU Circular No.8683
3 March 2006
RS OPHIUCHI
--------------------------------------------------------------------------------
J.-U. Ness and S. Starrfield, Arizona State University; J. J.
Drake, Smithsonian Astrophysical Observatory; M. Orio, Istituto
Nazionale di Astrofisica and University of Wisconsin; M. F. Bode,
Liverpool John Moores University; T. J. O'Brien and R. J. Davis,
University of Manchester; J. Osborne and K. L. Page, University of
Leicester; G. Schwarz, West Chester University; J. Krautter,
University of Heidelberg; A. Evans, Keele University; S. P. S.
Eyres, University of Central Lancashire; and R. Gehrz and C.
Woodward, University of Minnesota, report on the first high-
resolution x-ray spectra of the outburst of the recurrent nova RS
Oph (cf. IAUC 8671), obtained on Feb. 26 (two weeks after the
beginning of the outburst). The Chandra X-ray Observatory High
Energy Transmission Grating and ACIS-S detector observed RS Oph for
10000 s in the wavelength range 0.15-2.5 nm, revealing a rich
emission-line spectrum dominated by resonance lines of He-like and
H-like ions of Fe, S, Si, Mg, and Ne superimposed on a strong
continuum. The lines seen indicate that a wide range of plasma
temperatures have been observed: the coolest transition detected
is the O VIII Lyman_alpha doublet at 1.897 nm (emissivity peak at T
= 3 MK), while the hottest is the Fe XXV 1s2p-1s2 resonance line
(emissivity peak at T = 60 MK). Lines show broadening
corresponding to approximately 2000 km/s at half maximum, with
systematic blueshifts amounting to approximately 500 km/s (Si XIV,
Mg XII, and Ne X) and 1000 km/s (O VIII).
J. D. West, Mulvane, KS, reports the following infrared
magnitudes of RS Oph obtained with a 0.25-m reflector (+ Optec SSP-4
Photometer): Feb. 13.4715 UT, J = 2.71 +/- 0.02; 13.4715, H = 2.36
+/- 0.01; 14.4715, J = 3.06 +/- 0.01; 14.4715, H = 2.67 +/- 0.01;
23.4729, J = 4.80 +/- 0.22; 23.4729, H = 4.34 +/- 0.06; 27.5306, H
= 4.74 +/- 0.12.
