FOLLOW UP OBSERVATIONS OF SDSS AND CRTS CANDIDATE CATACLYSMIC VARIABLES^*

This CV has a peculiar nature that has defied classification. It was classified as a dwarf nova when it was discovered (Miller 1971), but the light curve was peculiar in showing long periods at quiescence near 17.5 mag and also what appeared to be standstills about 1 mag below maximum light that would classify it as a Z Cam star (Warner 1995). Bruch & Schimpke (1992) obtained spectra which showed the typical Balmer emission lines of a CV. Outbursts are relatively rare and have not been well studied in the past. In 2011 May, V1363 Cyg underwent its first outburst since 1952 as reported by vsnet (Oshima 2011a). Quasi-periodic oscillations (QPOs) from 8.5–10.5 minutes and an amplitude of 0.05 mag were reported from May 8 to June 1. On May 30, a longer QPO at 28.8 minutes was observed (Oshima 2011b). Our light curves in May (Figure 2) show the QPOs, with changes in amplitude noticeable in the longer light curves of May 13 and 24.

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This counterpart to an X-ray object in Andromeda was found by MASTER and reported by Denisenko (2013a) with archival images showing variability from 15th–19th mag. A further alert (Denisenko 2013b) reported unusual behavior at a mid-state between 2013 September 16–25 that could be indicative of an active Polar. Our 2.8 hr of photometry on 2013 October 29 (Figure 3) show a double-humped modulation at a period of 109 minutes. The velocities measured from our 1.5 hr of APO time-resolved spectra on 2013 October 2 give a best fit to a sinusoid with period of 103 minutes and a semi-amplitude of 54 km s⁻¹ (Table 3 and Figure 3). The lack of a high excitation line of He ii, combined with the low semi-amplitude of the radial velocity curve, argue for this object being a normal low-inclination dwarf nova rather than a Polar.

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This 19th mag CV was observed in order to search for possible white dwarf pulsations, as its SDSS spectrum (Szkody et al. 2011) showed broad Balmer absorption lines flanking the emission lines. This type of spectrum is typical in the 16 known accreting white dwarf pulsators. However, our four light curves in 2011 May did not reveal any periodic feature that could be ascribed to either pulsation or orbital motion.

The SDSS spectrum of this 17th mag object showed weak Balmer emission lines and a broad hump feature near 5200 Å that implied an origin as a cyclotron harmonic from a magnetic white dwarf (Szkody et al. 2011). Time-resolved spectra revealed a large (∼400 km s⁻¹) semi-amplitude variation of the Hα and Hβ lines with orbital periods of 110 and 122 minutes, respectively, which was consistent with a Polar nature. Our three nights of photometry in 2011 June shown in Figure 4 corroborate this Polar identification, but also show interesting changes during the week timespan. On June 5, a very large (2 mag) hump is visible. This feature is typical of an accretion pole passing through the line of sight, such as occurs in the Polar VV Pup (Warner & Nather 1972; Liebert et al. 1978), but the light increases after the passage of the pole. The next night, June 6, shows the hump with less amplitude but longer duration, while four days later, on June 10, the system has transitioned to most of the time spent in the bright state. This is somewhat reminiscent of the light curves of the Polar CSS071126+440405 (Thorne et al. 2010), which was interpreted as sporadic mass transfer. If the increased mass transfer moves the accretion zone so that it is no longer eclipsed by the white dwarf, the light curve would not have the low segment visible on June 5. The changes in the light curve make the determination of a photometric orbital period difficult, but the features present on June 5 and 6 are most consistent with a period near 100 minutes.

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The spectra obtained in 2011 May and June (Table 2 and Figure 1) also reveal significant changes in accretion. On May 15, the system was in a low state with a featureless spectrum, while the spectra on June 9 and 10 show a flux increase by a factor of two as well as increased Balmer line strengths over those in the SDSS spectrum. If the broad hump around 4200 Å is a cyclotron hump, its presence together with the one at 5300 Å in the SDSS spectrum would imply a field strength of ∼65 MG for harmonics of 4 and 3 (Wickramasinghe & Ferrario 2000).

While the SDSS spectrum of this g = 17.7 mag source shows strong He ii (Szkody et al. 2005), the light curve obtained over 1.4 hr on 2013 July 26 shows no prominent feature, only flickering of a few tenths in magnitude.

The SDSS spectrum of this 19.9 mag object (Szkody et al. 2009) shows Balmer absorption surrounding its emission lines. The five nights of photometry in 2011 May–June (Figure 5) show a broad feature with an amplitude near 0.08 mag and a period of 75–78 minutes.

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This g = 16.8 mag system also shows a prominent He ii line in its SDSS spectrum (Szkody et al. 2006). Its light curve on two nights in 2013 July (the longest timespan is shown in Figure 6) shows a 10% amplitude flickering as well as a possible hump, but further photometry is needed to determine if this is a periodic occurrence.

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This object was discovered in outburst at V = 14 as ASASSN-13cg on 2013 August 27 and matched with a blue SDSS g = 18.3 object (Stanek 2013), while later vsnet posts suggested a possible AM CVn object. Observations by Littlefield reported by Kato (2013b) revealed a superhump period of 1.4 hr and shallow (0.1 mag) eclipses. Our light curve obtained two months later (2013 October 29) near quiescence (Figure 7) shows some variability near 37 minutes with an amplitude of 0.4 mag, although better signal-to-noise ratio (S/N) and a longer timespan will be needed to ascertain if this is related to the orbital period.

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This g = 18.9 mag CV appears in DR10 of the SDSS III release. The SDSS spectrum is shown in Figure 8. The deep absorption in the Balmer lines, along with the broad absorption flanking the emission, is indicative of a system at high inclination and with a low mass transfer rate. Our follow up photometry during 2011 June (Figure 9) confirms the high inclination by showing two eclipses on each night. While the eclipses are not well resolved at our time resolution of 194 s between exposures, the combination of the two nights yields an orbital period of 76 ± 2 minutes.

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An outburst of this CRTS CV on 2013 June 4 at 17.5 mag was reported by vsnet (Kato 2013a). A light curve showed a prominent single hump feature with a period of 96.9 minutes. Our light curve shows a similar feature four months later (Figure 10). The large amplitude (1.5 mag) is indicative of a Polar nature for this object.

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Our KPNO spectra obtained on 2013 September 5 (Figure 1) shows a prominent He ii line. The velocities from the 82 minute time-resolved spectra were fit to a sine curve with the period fixed at 96.9 minutes (Figure 10). The resulting large K amplitudes near 300 km s⁻¹ (Table 3) are consistent with a Polar. The SDSS photometry obtained in 2009 October gives a fainter magnitude (g = 18.65) and blue colors (u − g = 0.10, g − r = 0.02), which are not consistent with the usual red colors of a Polar. However, the system may have been in a low state at the time of the SDSS observations, similar to the low state in EF Eri when the white dwarf dominates the optical light (Wheatley & Ramsay 1998). Polarimetric measurements would confirm that this object harbors a magnetic white dwarf.

The CSS light curve of this object shows a bright measurement at 13.2 on 2010 June 15. The rest of the time it resides near 17.6 mag, with a large scatter indicative of orbital variability. This object exists in the SDSS photometric database with blue colors (g = 17.51, u − g = 0.08, g − r = −0.10). Calibrated V, R, I images by TS provide a comparable V magnitude of 17.48 and V − R = 0.13. Our KPNO spectra obtained in 2010 September (Figure 1) show prominent deep central absorption in the Balmer emission lines, indicative of a high inclination. Our KPNO photometry obtained nine months later (Figure 11) reveals a large-amplitude (0.3 mag) hump feature followed by dips (near UT times of 9 and 10.7 hr) that hint at eclipses, but the 4 minute integration times do not allow resolution of this feature. A periodogram of these data gives a period of 104 minutes. Using the 12 time-resolved spectra obtained over 2 hr on 2010 September 16, we attempted a radial velocity solution using centroids, Gaussians, and the line wings of Hβ. Due to the complexity of the line shape and the less than ideal S/N, a good solution could not be determined. The values obtained by fixing the period at values between 100–120 minutes are listed in Table 3. The semi-amplitudes are typical for dwarf novae but improved data will be needed to pin down the period. Spectra in the red can determine if the secondary is visible.

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Drake et al. (2009b) identified this 18th mag ROSAT source as a CV when the CSS measured it at 13.3 mag in 2009 September. Our KPNO blue spectra over 73 minutes reveals a typical dwarf nova (Figure 1) with a period near 100 minutes and a K semi-amplitude near 70 km s⁻¹ (Figure 12, Table 3).

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The CSS identifies a 1 mag variation in this g = 15.58 mag SDSS object. The blue colors (u − g = 0.06, g − r = 0.10) are consistent with a CV. The KPNO blue spectra obtained in 2013 September show the strong Balmer emission lines of a dwarf nova and the 11 time-resolved spectra over 113 minutes on September 6 are fit with a period near 80 minutes and a K semi-amplitude near 60 km s⁻¹ (Table 3, Figure 13). While the photometric amplitude is very low, the other characteristics are typical of a dwarf nova. It is possible that the variation caught by CSS was not an outburst but merely a sporadic accretion event, as objects with such short orbital periods often have outburst frequencies that are tens of years.

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This g = 18.5 system showed strong Balmer emission lines in its SDSS spectrum (Szkody et al. 2004). Our 82 minutes of time-resolved spectra on 2013 February 5 reveals a low K semi-amplitude and an orbital period near 100 minutes (Figure 14, Table 3).

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The SDSS spectrum of this bright 16th mag system shows broad absorption with central narrow emission and was suggested as a possible pre-CV (Szkody et al. 2011). Our 126 minutes of time-resolved spectra on 2011 May 16 showed no significant radial velocity variation during that interval. The system likely has a long orbital period and/or a low inclination.

This object was identified in the SDSS spectra at quiescence (Szkody et al. 2006) as a high-inclination, eclipsing system with a period of 84 minutes. A vsnet alert by Maehara (2011) reported the CSS detection of this system at an outburst mag of 15 (2.5 mag brighter than quiescence) on 2011 June 11. We obtained four spectra on June 13 and eight on June 14 in order to search for a line component that could be from the irradiated secondary star and yield the velocity amplitude of the secondary. The spectra (Figure 1) show much stronger Balmer lines and a much larger flux in the He ii line than the quiescent spectra. The Hβ/He ii flux and equivalent width ratios on June 13 were 1.25 and 1.29, respectively, whereas they were 15 and 7 in the quiescent SDSS spectra. On June 13, the He ii line does show a prominent red peak when the Balmer lines have a prominent blue peak (Figure 1). However, the four spectra were not enough to resolve a velocity curve, and the next night the peaks in the lines are similar in phase. The radial velocity curves from June 14 (Table 3) have higher amplitudes than the quiescent data (a factor of two for Hβ), implying an origin closer to the white dwarf.

CSS found an outburst of this object on 2010 September 10. Our KPNO spectrum on September 12 shows the typical Balmer absorption lines of an accretion disk at outburst while the Palomar spectrum on September 18 shows the lines in emission, indicating that it was a short outburst and that the system was already declining to quiescence. The SDSS quiescent g magnitude is 20.5. While the integration time is long, so there is likely velocity smearing, the asymmetric nature of the lines may indicate a prominent hot spot, but a larger telescope is needed for orbital resolution.

The spectrum of this system near quiescence shows an interesting sharp peak in the broad Balmer emission lines. This could be indicative of irradiation of the companion or a hot spot on the accretion disk.

While these objects are very faint at quiescence, the broad lines of Hβ and Hγ are visible. The quiescent g magnitude of SDSS0058+28 is 19.2.

Szkody et al. (2011) identified this object as a possible CV but with very narrow Balmer lines and a very blue continuum. The KPNO spectrum is very similar to the SDSS one, but extends blueward by 100 Å. It is possible that this system is a hot star with an irradiated companion.

The asymmetric line shape with a sharp narrow component is typical of CVs with a prominent hot spot. The SDSS quiescent g magnitude is 19.8.

This object also displays the asymmetric profiles and peaks associated with a hot spot component. TS have time-resolved red spectra obtained four months after our KPNO data from which they obtained an orbital period of 1.8 hr.

TS obtained time-resolved red spectra in 2011 March that determined an orbital period of 8.9 hr. Our spectrum shows the blue wavelengths of this source.

The spectrum shows prominent, very broad, and doubled Balmer emission, indicating a fairly high-inclination system. TS obtained four images on 2011 June at V = 20.83 showing very blue colors (B − V = −0.96). The SDSS photometry shows g = 18.5.

One year after their outbursts, these objects display typical CV spectra with strong, broad Balmer emission. The SDSS photometry provides g magnitudes of 19.6, 18.9, and 18.5 for these three objects.