NEAR-INFRARED SPECTROSCOPY OF V1493 AQUILAE AND V4642 SAGITTARII: TWO NOVAE WITH UNUSUAL SPECTRAL FEATURES

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1 The Astronomical Journal, 128: , 2004 July # The American Astronomical Society. All rights reserved. Printed in U.S.A. NEAR-INFRARED SPECTROSCOPY OF V1493 AQUILAE AND V4642 SAGITTARII: TWO NOVAE WITH UNUSUAL SPECTRAL FEATURES Catherine C. Venturini, Richard J. Rudy, David K. Lynch, and S. Mazuk The Aerospace Corporation, M2/266, P.O. Box 92957, Los Angeles, CA 90009; Catherine.Venturini@aero.org and R. C. Puetter Center For Astrophysics and Space Sciences, C-0111, University of California, San Diego, La Jolla, CA 92093; and Pixon LLC, 9295 Farnham Street, San Diego, CA Received 2004 February 19; accepted 2004 March 31 ABSTRACT We present m spectroscopy of two novae with uncommon spectral features at different stages in their decline after outburst. Nova Aql 1999 No. 1 ( V1493 Aql) was a very fast nova that initially exhibited a rapid decline in brightness that flattened by day 20 and actually reversed to show an unusual secondary peak. The nearinfrared spectrum was observed during this secondary peak at 46 days after initial peak brightness. Blended lowexcitation lines such as H i Brackett and Paschen and O i largely populated the spectrum, which also showed a strong continuum declining monotonically toward the red ( m). He ii lines were just beginning to emerge. The overall spectral appearance was much more representative of the period a few days after outburst. A possible explanation for this, and the secondary peak in the visible light curve, is that the nova experienced a second period of mass loss, but of a more continuous rather than explosive nature. Nova Sgr 2000 (V4642 Sgr) was a moderately fast nova, observed 160 days after peak brightness. High-excitation lines, including coronal lines, were present in the spectrum. However, their profiles were distinctly different from those of the lower excitation lines. Also present were four emission lines that have only recently been detected in the spectra of novae and which remain unidentified. Key words: infrared: stars line: identification novae, cataclysmic variables techniques: spectroscopic 1. INTRODUCTION V1493 Aquilae was discovered on 1999 July UT by A. Tago (Nakano et al. 1999) at the coordinates R:A: ¼ 19 h 07 m 36 s :90 and decl: ¼þ B2 (J2000) with an observed visual magnitude equal to 9 (Moro et al. 1999). On 1999 July 14.6 UT, Ayani et al. (1999) obtained a low-resolution spectrum showing strong, broad H and H lines with a FWHM of 3400 km s 1. Tomov et al. (1999) also obtained a spectrum, on 1999 July 15.9 UT, showing Fe ii emission lines and Balmer lines. The equivalent width of 0.24 nm for the Na i doublet at 589 nm suggested a large reddening. By 1999 August 3.89 UT, approximately 21 days after initial discovery, the nova was already at a visual magnitude equal to 13.0 (Bouma et al. 1999). Bonifacio et al. (2000) also found that V1493 Aql underwent a secondary increase in visual brightness around the time of the observations reported here. Arkhipova et al. (2002) also observed V1493 Aql between 1999 July and November in the optical wavelength region. Early spectra exhibited the same emission lines as mentioned above, but by 1999 September the spectra showed that V1493 Aql had entered into the nebular phase, with He i and [O i] lines emerging. By 1999 November, only hydrogen lines and forbidden lines of oxygen and nitrogen remained. V4642 Sagittarii was discovered on 2000 February UT by Sakurai at J2000 coordinates R:A: ¼ 17 h 55 m 09 s :84 and decl: ¼ with a visual magnitude equal to 10.5 (Nakano et al. 2000). Wagner et al. (2000) obtained a spectrum in the optical wavelength region on 2000 February UT that was typical of classical novae in the early decline phase. The spectrum showed broad emission lines from the hydrogen Balmer series, H and H emission lines with P Cygni profiles, 405 and Fe ii lines superposed on a red continuum. The measured width (FWHM) of H emission was 1530 km s 1. On 2000 February UT, Ashok et al. (2000) obtained spectrophotometry in the near-ir, which exhibited strong H i emission lines at Br, Br10 Br15, Pa,andPa.TheLy fluoresced O i line at m was also seen at significant strength. The FWHM was about 1900 km s 1. From these early observations, it seems that V4642 Sgr can be classified as an Fe ii class nova (Williams 1992). In this paper, we present near-ir spectroscopic observations of these two novae. The details of the observations of V1493 Aql and V4642 Sgr will be discussed in the next section, followed by a section that presents the near-ir spectrum, light curve, and estimations of reddening and distance for each nova and also considers the unique attributes of each nova and their relation to previous novae. 2. OBSERVATIONS All observations were made with the Aerospace Corporation s Near Infrared Imaging Spectrograph (NIRIS) on the University of California s Lick Observatory 3 m Shane Telescope (Rudy et al. 1999). The spectrograph incorporates two separate channels, divided at 1.38 m by a beam splitter, to provide nearly continuous coverage between 0.8 and 2.5 m. Each channel has its own collimator, grating, camera, and HgCdTe detector array. The arrays are two-quadrant NICMOS3 devices providing 256 channels in the spectral dimension and 128 in the spatial at a scale of 1 00 pixel 1. Each channel has nearly constant spectral resolution. A 2B7 slit width was used, resulting in a resolution of 16 8 for the blue channel and 37 8 for the red. To remove the background, spectra were acquired

2 406 VENTURINI ET AL. Vol. 128 TABLE 1 Standard Comparison Stars TABLE 2 V1493 Aquilae Line List from 1999 August UT Date (UT) Star Spectral Type V (mag) K (mag) Wavelength a (m) ID F/F(Pa) b 1999 Aug HR 7260 G5 V Jul HR 6496 F7 V at two locations separated about along the slit. Wavelength calibration was achieved by using features from helium and argon emission-line lamps, telluric absorption features, and OH lines from the night sky. The observations were reduced by dividing the spectrum by that of a nearby comparison star to remove instrumental response and the effects of atmospheric absorption. Table 1 lists the spectral type and derived K magnitude for each comparison star used during the observations. The K magnitude is based on Koornneef s (1983) calculations of V K and the visual magnitude, V, of each comparison star. Flux calibration was performed by taking the spectral shape from Kurucz (1991) appropriate for each star and setting the level based on the derived K magnitude. 3. RESULTS AND DISCUSSION 3.1. Nova V1493 Aql 1999 No. 1 The near-ir spectrum of V1493 Aql taken on 1999 August UT is shown in Figure 1, with the emission lines identified in Table 2. Figures 2 and 3 show the blue ( m) and red ( m) regions of the spectrum with the major emission lines identified. From the light curve in Figure 4, the secondary peak was observed around 1999 August UT (Hanzl 1999). This places our data about 8 days after the noticeable secondary peak. The spectrum consisted of broad, N i O i N i ? ; ; , H i Pa9 + O i +Ni H i Pa ? N i ? H i Pa , [ N i] ? He i H i Pa ; O i +Ni N i N i H i Pa O i H i Br H i Br H i Br H i Br H i Br He i H i Br 0.39 a For lines that are uidentified, the wavelengths are the measured wavelengths. Otherwise all wavelengths are laboratory wavelengths as measured in air. b The flux for F(Pa)is1:45 ; Wcm 2.TheuncertaintyinF/F(Pa) is 10%. Fig. 1. V1493 Aql near-ir spectra from 1999 August UT, approximately 46 days after peak brightness.

3 No. 1, 2004 TWO NOVAE 407 Fig. 2. The m region of V1493 Aql.Lines of O i, H i, and N i dominate this spectral region. [ N i] is also present. blended lines with a FWHM of approximately 4000 km s 1, and its continuum showed a decrease toward the red region. Because of the broad lines and ragged tops of the lines, it is difficult to identify all of the lines present, but it is evident that the O i lines at and m were the dominant lines, followed by the H i Paschen and Brackett lines, He i at m, and various lines of N i. The low-excitation forbidden line [N i] at m could possibly be present. Neutral carbon was not present in this spectrum, which could indicate an underabundance of C i in the ejecta or that the excitation was just high enough to singly ionize carbon while leaving nitrogen neutral. The J, H, andk magnitudes were 8.4, 8.2, and 7.7, respectively. From the light curve (Fig. 4), generated from AAVSO data, we adopted the date of peak brightness to be 1999 July 15.5 UT, or JD 2,451,375. This corresponds to an apparent visual magnitude of V ¼ 10:0 0:5. As noted on the light curve, our observations were taken about 46 days after peak brightness. Whereas Bonifacio et al. (2000) calculated t 2 on the order of 3 days, our calculations found t 2 on the order of Fig. 3. The m region of V1493 Aql. H i Brackett lines are the strongest in this spectral region. Fig. 4. Light curve of V1493 Aql. Note the strong secondary peak approximately 48 days after initial peak brightness. 7daysandt 3 on the order of 23 days. Clearly, V1493 Aql was a very fast nova (Payne-Gaposchkin 1957). It is also apparent from the light curve that V1493 Aql had an unusual increase in brightness during the middle of 1999 August, about 48 days after initial peak brightness, with a duration of 40 days. This places the timing of our observation within days of the secondary brightness peak. Photometric observations from Bonifacio et al. (2000) were taken between 1999 August 5 and 15 at the beginning of the nova outburst. Their visual magnitude measurements showed evidence for small-amplitude oscillations throughout the initial phase of the nova, including the secondary brightness peak. Although oscillations in the visual magnitude have been seen before in other novae, the long-lasting secondary brightness peak is unusual in terms of duration and magnitude (Bonifacio et al. 2000). For example, photometry of the recurrent nova T CrB showed a secondary maximum about100 days after initial brightness, and V533 Her showed small-amplitude brightening with smaller duration and range in magnitude (Bonifacio et al. 2000; van den Bergh & Younger 1987). Bonifacio et al. s photometry analysis found that at peak brightness B V þ0:4, near the secondary maximum B V þ1, and the following decline was approximately B V þ0:7 (Bonifacio et al. 2000). Generally, novae increase in temperature as they evolve, as a result of the decrease in the radius of the surrounding shell and opacity. This allows the hotter interior layers to be exposed (Bode & Evans 1989). In the case of V1493 Aql, the temperature decreased from peak brightness through subsequent phases. It is probable that the secondary outburst apparent in the light curve was due to an additional but slow increase in the material being expelled from the surface of the white dwarf. This can be attributed to the fact that the spectrum consisted of very low excitation lines over 40 days after initial outburst for a very fast nova. It also is consistent with the lower temperature measured by Bonifacio et al. (2000) after the secondary outburst maximum. Dust formation could also account for the change; however, this seems unlikely, since there was no indication of dust in the light curve or spectra. The approximate values for absolute magnitude and distance were obtained from our observations and Bonifacio et al. (2000). From the M v -t 2 relation of Della Velle & Livio (1995), the absolute visual magnitude is M v ¼ 8:83 0:22. The

4 408 VENTURINI ET AL. Vol. 128 Fig. 5. V4642 Sgr near-ir spectra from 2000 July UT, approximately 160 days after peak brightness. absolute blue magnitude is M b ¼ 8:22 0:74 using the M b -t 3 relation from Pfau (1976). On 1999 July UT, near our adopted date of peak brightness, Zejda (1999) found V ¼ 10:59 0:01 and B V ¼ 0:40 0:02, which correspond to an apparent blue magnitude of about m b ¼ 10:99 0:03. Using the observed O i flux ratios for the , , and m lines in Table 2, the color excess is E(B V ) ¼ 0:57 0:14. The color excess was calculated assuming the extinction properties of dust described by the reddening curve of Draine (1989). From the color excess, the visual extinction is A v ¼ 1:77 0:43. Using M v ¼ 8:83, V max ¼ 10:00, and A v ¼ 1:77, the distance is then d ¼ 25:82 1:81 kpc. Bonifacio et al. (2000) also calculated the distance for V1493 Aql using three different approaches and found the distance to range from 17.6 to 40.4 kpc. Because of the strange behavior of this nova, as evident in the light curve, it is difficult to determine an accurate distance. As Bonifacio et al. (2000) pointed out, if the distance is over 25 kpc then the nova is well out of the Galaxy Nova V4642 Sggr 2000 The spectrum of V4642 Sgr was taken on 2000 July UT approximately 160 days after peak brightness and is shown in Figure 5. The emission lines are identified in Table 3. Figures 6 and 7 show the blue ( m) and red ( m) region of the spectrum with the major emission lines identified. The spectrum had a relatively flat continuum with no evidence of thermal dust emission in the longer wavelengths. The J, H, andk magnitudes determined from the spectrum are 12.5, 12.7, and 11.6, respectively. The emission lines had a FWHM on average of km s 1.Hei at m dominated the spectrum, followed by H i Pa at m. Many of the hydrogen Paschen and Brackett lineswerepresent,aswellascoronallinessuchas[siix] at m, [Ca viii] at m, and [S viii] at m. Of the low-excitation features, only [ N i] at m was distinguishable. A unique feature in the spectrum of V4642 Sgr is the noticeable shape of the coronal emission lines compared with the lower excitation lines. In Figure 8, H i Pa at m and [Ca viii] at2.3205m are plotted together in velocity space. The coronal line has an unusual double-peaked shape whereas the hydrogen line has a more Gaussian appearance. This double-peaked shape was also seen in the other coronal lines, [S viii] at0.9913m, [Si ix] at m, and [Si vi] at m. As usual, common but unknown lines were present in the spectra at approximately , , , and m. Accurate wavelengths were presented for these lines by Rudy et al. (2002), who measured them in the comparatively narrow-lined nova V723 Cas. Rudy et al. considered a number of possible identifications for these features but could find none that were satisfactory. The lines are seen in a number of other novae (e.g., Lynch et al. 2000, 2001; Venturini et al. 2002). These novae were similar to V4642 Sgr in that they had He ii lines and coronal lines. It is probable that these unidentified lines in the spectrum of V4642 Sgr are of a high excitation but not as high as the coronal lines. The light curve for V4642 Sgr is shown in Figure 9. For our calculations we have adopted a date of peak brightness of 2000 February 11.5 UT, or JD 2,451,586, which corresponds to an apparent visual magnitude of V ¼ 11:20 0:50. As is evident in the light curve, the observations of V4642 Sgr were sparse after its first detection, and thus it is hard to get a firm

5 No. 1, 2004 TWO NOVAE 409 TABLE 3 V4642 Sagittarii Line List from 2000 July UT Wavelength a (m) ID F/F(Pa) b He ii O i H i Pa H i Pa H i Pa H i Pa H i Pa He ii H i Pa [S viii] , H i Pa +Heii [ N i] He i H i Pa c O i , He ii d , [Si ix] +Hei H i Pa O i He ii d He ii H i Br H i Br H i Br H i Br He i H i Br H i Br [Si vi] He i c , He i H i Br He ii [Ca viii] ? [Si vii] 0.48 Fig. 6. The m region of V4642 Sgr.H i Paschen and helium lines are present, as are coronal lines of [S viii] at0.9913m and[siix] at m. An unidentified line is also present at m, which was seen in the spectrum of Nova Cas 1995, discussed in Rudy et al. (2002). 46 days after peak brightness, and V4642 Sgr a moderately fast nova observed 160 days after the initial peak. The spectrum of each nova exhibited H i Brackett and Paschen lines,aswellasoi lines, which are very common in the early spectra of classical novae. Otherwise each nova s spectrum had unique characteristics. V4642 Sgr exhibited high-excitation coronal lines, but the line profiles were distinctly different from the lower excitation lines. Several recently detected but currently unidentified lines were present as well. V1493 Aql had a distinctive light curve with an unusual secondary outburst. The spectrum observed about this time was dominated by broad, blended low-excitation lines and is possibly indicative of a second period of mass loss. a For lines that are unidentified, the wavelengths are the measured wavelengths. Otherwise all wavelengths are laboratory wavelengths as measured in air. b The flux for F(Pa) is1:20 ; Wcm 2.Theuncertaintyin F/F(Pa) is10%. c See Rudy et al d Unidentified line, common in novae. grasp of the shape of the light curve and behavior of the nova s decline rate. We have measured the speeds to be t 2 ¼ 49 days and t 3 ¼ 86 days, which would make V4642 Sgr a moderately fast nova (Payne-Gaposchkin 1957). The absolute visual magnitude is estimated to be M v ¼ 7:10 0:04, and M b ¼ 7:19 0:73. Using the O i lines, the color excess is E(B V ) ¼ 1:51 0:16 with a visual extinction of A v ¼ 4:68 0:49. Using M v ¼ 7:10, V max ¼ 11:20, and A v ¼ 4:68, the distance is then d ¼ 5:28 0:10 kpc. 4. SUMMARY AND CONCLUSION In this paper we present two novae with unusual spectral features. V1493 Aql was a very fast nova that we observed Fig. 7. The m region of V4642 Sgr. H i Brackett lines and helium lines are present with coronal lines of [Ca viii]at m and [Si vii] at m. Another unidentified line is present at m, as discussed in Rudy et al. (2002).

6 410 VENTURINI ET AL. Fig. 9. Light curve of V4642 Sgr. Fig. 8. Expanded view of H i Pa at m and [Ca viii]at m in velocity space. [Ca viii] and other coronal lines in this spectrum show a double peak that is not seen in the lower excitation emission lines. We would like to thank the telescope operators K. Baker and W. Earthman at Lick Observatory and T. Armstrong and T. Tessensohn for their help in acquiring data. Light-curve data were obtaineded from the AAVSO International Database, which is based on observations submitted to the AAVSO by variable star observers worldwide. This work was supported by The Aerospace Corporation s Independent Research and Development program and by the US Air Force Space and Missile Systems Center through the Mission Oriented Investigation and Experimentation program, under contract FA C R. C. P. acknowledges support from NASA and Pixon LLC. Arkhipova, V. P., Burlak, M. A., & Esipov, V. F. 2002, AZh Pisma, 28, 118 (English transl. Astron. Lett., 28, 100) Ashok, N. M., Kamath, U. S., Chandrasekhar, T., & Tej, A. 2000, IAU Circ Ayani, K., Kawabata, T., & Tago, A. 1999, IAU Circ Bode, M. F., & Evans, A. 1989, Classical Novae (Chichester: Wiley) Bonifacio, P., Selvelli, P. L., & Caffau, E. 2000, A&A, 356, L53 Bouma, R., Reszelski, M., Schmeer, P., Hornoch, K., & Lehký, M. 1999, IAU Circ Della Valle, M., & Livio, M. 1995, ApJ, 452, 704 Draine, B. T. 1989, in Infrared Spectroscopy in Astronomy, ed. B. H. Kaldeich (ESA SP-290) (Paris: ESA), 93 Hanzl, D. 1999, IAU Circ Koornneef, J. 1983, A&A, 128, 84 Kurucz, R. L. 1991, in Precision Photometry: Astrophysics of the Galaxy, ed. A. G. D. Philip, A. R. Upgren, & K. A. Janes (Schenectady: L. David), 27 Lynch, D. K., Rudy, R. J., Mazuk, S., & Puetter, R. C. 2000, ApJ, 541, 791 Lynch, D. K., Rudy, R. J., Venturini, C. C., Mazuk, S., & Puetter, R. C. 2001, AJ, 122, 2013 (erratum 122, 3509) REFERENCES Moro, D., Munari, U., Tomov, T., & Henden, A. 1999, Inf. Bull. Variable Stars, No Nakano, S., Sakurai, Y., Kushida, Y., Kushida, R., Mattei, J., & Malatesta, K. 2000, IAU Circ Nakano, S., Tago, A., & Nakamura, A. 1999, IAU Circ Payne-Gaposchkin, C. H. 1957, The Galactic Novae (Amsterdam: North- Holland) Pfau, W. 1976, A&A, 50, 113 Rudy, R. J., Puetter, R. C., & Mazuk, S. 1999, AJ, 118, 666 Rudy, R. J., Venturini, C. C., Lynch, D. K., Mazuk, S., & Puetter, R. C. 2002, ApJ, 573, 794 Tomov, T., Moro, D., & Munari, U. 1999, IAU Circ van den Bergh, S., & Younger, P. F. 1987, A&AS, 70, 125 Venturini, C. C., Rudy, R. J., Lynch, D. K., Mazuk, S., & Puetter, R. C. 2002, AJ, 124, 3009 Wagner, R. M., Bertram, R., & Starrfield, S. G. 2000, IAU Circ Williams, R. E. 1992, AJ, 104, 725 Zejda, M., Sáfár, J., Masi, G., Hájek, P., & Hanzl, D. 1999, IAU Circ. 7228

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