May 2025 - vsnet-alert - ooruri.kusastro.kyoto-u.ac.jp

[vsnet-alert 28069] ASASSN-25ca: new SU UMa-type dwarf nova
by Yusuke Tampo 30 May '25

30 May '25

ASASSN-25ca: new SU UMa-type dwarf nova ASAS-SN reported ASASSN-25ca on 2025-05-20 at g=14.1. https://www.aavso.org/vsx/index.php?view=detail.top&oid=10848671 Berto Monard and Josch Hambsch reported the time-resolved observations of ASASSN-25ca. Their observations on 29 May show ordinary superhumps with a period of 0.0588(1) d. Observations on 27 May also show a hint of superhumps but the baseline was too short. Thus, ASASSN-25ca is a new SU UMa-type dwarf nova, and could be a WZ Sge-type based on its short superhump period, large outburst amplitude, and lack of previous outbursts. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow Yusuke TAMPO / 反保雄介 EMAIL: tampo(a)kusastro.kyoto-u.ac.jp ALT. EMAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28068] ASASSN-25bz: new SU UMa-type dwarf nova
by Yusuke Tampo 28 May '25

28 May '25

ASASSN-25bz: new SU UMa-type dwarf nova ASASSN-25bz (=AT 2025lkr) was discovered at 14.8 mag on 20 May by ASAS-SN. The suggested outburst amplitude is ~8 mag according to the VSX. ASAS-SN reported to the TNS that this could be a classical nova based on its low Galactic latitude b~-2.0 deg. https://www.aavso.org/vsx/index.php?view=detail.top&oid=10848672 I obtained the time-resolved observations of ASASSN-25bz with the SAAO/Lesedi telescope on 26 and 27 May. Its light curve shows a prominent ordinary superhump with an amplitude of 0.15 mag and a period of ~0.0561(1) d (1-d aliases are possible). The optical spectrum obtained on 23 May with the SAAO/Lesedi telescope is dominated by Balmer absorption lines. Thus, I conclude that ASASSN-25bz is a new SU UMa-type dwarf nova. The system is around 15.6 mag. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow Yusuke TAMPO / 反保雄介 EMAIL: tampo(a)kusastro.kyoto-u.ac.jp ALT. EMAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28066] TCP J18513997+3522412: large-amplitude modulation, possibly eclipsing WZ Sge-type dwarf nova?
by Yusuke Tampo 27 May '25

27 May '25

TCP J18513997+3522412: large-amplitude modulation, possibly eclipsing WZ Sge-type dwarf nova? TCP J18513997+3522412 was discovered by Y. Nakamura on 22nd May at 13.7 mag (unfiltered). The counterpart star in Pan-STARRS1 is r~20.5 mag, and thus the outburst amplitude is 6.8 mag. http://www.cbat.eps.harvard.edu/unconf/followups/J18513997+3522412.html https://www.aavso.org/vsx/index.php?view=detail.top&oid=10848644 Sano-san reported the time-resolved observations of this object. Although the baseline was just one hour, the light curve shows a large-amplitude modulation of ~0.35 mag. This is likely either an ordinary superhump in a SU UMa-type dwarf nova or even a large-amplitude early superhump + eclipse in an eclipsing WZ Sge-type dwarf nova. Further time-resolved observations with longer baselines are encouraged. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow 反保雄介 Yusuke TAMPO MAIL: tampo(a)kusastro.kyoto-u.ac.jp MAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28065] TCP J02472889+6758170 = Gaia DR3 517539710877791488
by Yusuke Tampo 26 May '25

26 May '25

TCP J02472889+6758170 = Gaia DR3 517539710877791488 The NMW team discovered this transient at 13.0 mag (unfiltered), which is associated with the known variable star Gaia DR3 517539710877791488 with ~18.0 mag. They suggest that this could be an AM CVn star in outburst. Its blue color in the Pan-STARRS1 image also supports this suggestion, and TCP J02472889+6758170 is at least a CV in new outburst. http://www.cbat.eps.harvard.edu/unconf/followups/J02472889+6758170.html https://www.aavso.org/vsx/index.php?view=detail.top&oid=2841325 Time-resoved observations are encouraged. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow 反保雄介 Yusuke TAMPO MAIL: tampo(a)kusastro.kyoto-u.ac.jp MAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28064] ASASSN-25bu: new SU UMa-type dwarf nova
by Yusuke Tampo 23 May '25

23 May '25

ASASSN-25bu: new SU UMa-type dwarf nova ASASSN-25b was discovered by ASAS-SN on 2025-05-12.06. The outburst amplitude is ~8.3 mag according to the VSX. This object is currently ~17.5 mag. https://www.aavso.org/vsx/index.php?view=detail.top&oid=10848624 Josch Hambsch and the SAAO team have reported the time-seeries observations of ASASSN-25bu. Lesedi/Mookodi observations on 22 May showed probable superhumps with a period of ~0.0574 d and an amplitude of ~0.15 mag. Thus ASASSN-25bu is a new SU UMa-type dwarf nova. Considering its short superhump period, large outburst amplitude, and no previous outbursts, ASASSN-25bu might be a WZ Sge-type. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow 反保雄介 Yusuke TAMPO MAIL: tampo(a)kusastro.kyoto-u.ac.jp MAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28062] ZTF18acynctq = TCP J20402089+4915562 = ASASSN-25bt: new SU UMa star candidate
by Yusuke Tampo 20 May '25

20 May '25

ZTF18acynctq = TCP J20402089+4915562 = ASASSN-25bt: new SU UMa star candidate XOSS team via TOCP/TNS and ASAS-SN reported the 2025 outburst of this system, which is already known as ZTF18acynctq in its 2018 outburst. https://alerce.online/object/ZTF18acynctq http://www.cbat.eps.harvard.edu/unconf/followups/J20402089+4915562.html https://www.aavso.org/vsx/index.php?view=detail.top&oid=10848612 Its 2018 outburst lasted for ~15 days and showed a possible rebrightening in the ATLAS data. Thus the outburst cycle is ~2300 d. This system is currently ~16.0 mag, and time-resolved observations may detect superhumps. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow 反保雄介 Yusuke TAMPO MAIL: tampo(a)kusastro.kyoto-u.ac.jp MAIL: yusuke(a)saao.ac.za ----------------------------------------------

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[vsnet-alert 28061] V598 Sco: an eclipsing dwarf nova
by Rod Stubbings 19 May '25

19 May '25

V598 Sco is an active dwarf nova and listed in VSX as a UG star, range 14.9 - 17.0: V. [vsnet-chat 9283] lists V598 Sco as a Z Cam star. V598 Sco has been on my list for a number of years. On May 2 during an outburst I noticed a fading, then returned to normal brightness. A second fading occurred approx 3h 46 min later, which I observed back to normal. With a new outburst on May 18, I made 1-minute observations for 3h 29 minutes and caught another eclipse. Kept observations ongoing throughout the night and caught a second eclipse. The eclipse period was 3h 45 minutes. The first eclipse duration was 12 minutes and the second eclipse was 10 minutes. First eclipse: V598 SCO 2460814.0236 15.20 V598 SCO 2460814.0243 15.10 V598 SCO 2460814.0250 15.10 V598 SCO 2460814.0257 15.20 V598 SCO 2460814.0264 15.20 V598 SCO 2460814.0271 15.20 V598 SCO 2460814.0278 15.20 V598 SCO 2460814.0285 15.20 V598 SCO 2460814.0292 15.20 V598 SCO 2460814.0299 15.30 V598 SCO 2460814.0306 15.30 V598 SCO 2460814.0313 -15.30 V598 SCO 2460814.0319 -15.30 V598 SCO 2460814.0326 -15.40 V598 SCO 2460814.0333 -15.40 V598 SCO 2460814.0340 -15.40 V598 SCO 2460814.0347 -15.40 V598 SCO 2460814.0354 -15.50 V598 SCO 2460814.0361 -15.50 V598 SCO 2460814.0368 -15.50 V598 SCO 2460814.0375 -15.50 V598 SCO 2460814.0382 -15.50 V598 SCO 2460814.0389 -15.50 V598 SCO 2460814.0396 15.60 V598 SCO 2460814.0403 15.60 V598 SCO 2460814.0410 15.40 V598 SCO 2460814.0417 15.40 V598 SCO 2460814.0424 15.30 V598 SCO 2460814.0431 15.30 V598 SCO 2460814.0438 15.20 V598 SCO 2460814.0444 15.20 V598 SCO 2460814.0451 15.10 V598 SCO 2460814.0458 15.10 Second eclipse: V598 SCO 2460814.1833 14.90 V598 SCO 2460814.1840 15.00 V598 SCO 2460814.1847 15.10 V598 SCO 2460814.1854 15.10 V598 SCO 2460814.1861 15.10 V598 SCO 2460814.1868 15.20 V598 SCO 2460814.1875 15.30 V598 SCO 2460814.1882 -15.30 V598 SCO 2460814.1889 -15.30 V598 SCO 2460814.1896 -15.30 V598 SCO 2460814.1903 -15.30 V598 SCO 2460814.1910 -15.30 V598 SCO 2460814.1917 -15.40 V598 SCO 2460814.1924 -15.40 V598 SCO 2460814.1931 -15.40 V598 SCO 2460814.1938 -15.40 V598 SCO 2460814.1944 -15.40 V598 SCO 2460814.1951 15.50 V598 SCO 2460814.1958 15.50 V598 SCO 2460814.1965 15.40 V598 SCO 2460814.1972 15.40 V598 SCO 2460814.1979 15.30 V598 SCO 2460814.1986 15.30 V598 SCO 2460814.1993 15.10 V598 SCO 2460814.2000 15.00 V598 SCO 2460814.2007 15.00 V598 SCO 2460814.2014 14.90 V598 SCO 2460814.2021 14.90 V598 SCO 2460814.2028 14.90 -- Rod Stubbings Tetoora Road Observatory Victoria, Australia Honorary Associate member Astronomical Society of Australia Telescope: "Infinity" 22" f/3.8 stubbo(a)dcsi.net.au http://rodstubbingsobservatory.wordpress.com/

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[vsnet-alert 28060] TCP J19065629+4019093: new SU UMa-type dwarf novae and WZ Sge-type candidate
by Yusuke Tampo 11 May '25

11 May '25

TCP J19065629+4019093: new SU UMa-type dwarf novae and WZ Sge-type candidate TCP J19065629+4019093 was discovered by Y. Nakamura on 29th April, 2025, at 13.1 mag. S. M. Brincat, J. Hambsch, Itoh-san, T. Tordai, and Sano-san have reported the time-resolved observations of this new transient. The latest time-resolved observations on 9th May by S. M. Brincat report the presence of single-peaked superhumps with ~0.056 d. Thus TCP J19065629+4019093 is a new SU UMa-type dwarf nova. Taking into account this late (~10 d) appearance of superhumps, TCP J19065629+4019093 is likely a face-on WZ Sge-type dwarf nova. Further observations are encouraged to determine its superhump period. Best regards, Yusuke -- ---------------------------------------------- South African Astronomical Observatory, Postdoc fellow 反保雄介 Yusuke TAMPO MAIL: tampo(a)kusastro.kyoto-u.ac.jp MAIL: yusuke(a)saao.ac.za ----------------------------------------------

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