1No.118

May. 2023

Variable Star Bulletin
Low state in the post-nova V1315 Aql
Taichi Kato1
1 Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japantkato@kusastro.kyoto-u.ac.jp
Received 2023 May 19
Abstract
Using Asteroid Terrestrial-impact Last Alert System (ATLAS) and Zwicky Transient Facility (ZTF) data,
I found that the SW Sex star V1315 Aql entered a low state early in 2023. As far as I know, this is theﬁrst such an event since the discovery of this object with observations dating back to 1948. This object isrenowned for its nova shell and the nova explosion was estimated to occur 500–1200 yr ago, although no direct
detection of a nova eruption was present in the historical record. The present low state probably occurred as
the mass-transfer rate from the nova-irradiated secondary decreased secularly. The present low state would
provide an opportunity to study the secondary in detail, which has been hampered by the luminous accretion
disk in the past. I also provide the recent light curve of the classical nova LV Vul, which now shows high andlow states 50 yr after the nova eruption.

V1315 Aql was initially discovered as a variable star (=SVS 8130) by Metik (1961). During a search forultraviolet-excess objects, Downes et al. (1986) detected this object (KPD 1911+1212) and identiﬁed it to be aneclipsing cataclysmic variable. Its spectrum was that of a high-excitation old nova0 (this term was used slightly
diﬀerently from the modern meaning), and unusually singly peaked emission lines despite its high inclinationand the unusual behavior of the emission lines against the orbital phase already attracted attention. Downeset al. (1986) classiﬁed V1315 Aql to be a member of high-excitation (all eclipsing) old novae, including SW Sex,LX Ser, DQ Her, RW Tri and V363 Aur as a group. These unusual emission lines have been studied by manyauthors (Szkody 1987; Szkody and Piche 1990; Dhillon et al. 1991; Smith et al. 1993; Dhillon and Rutten 1995;
Hellier 1996). This object played an important role in establishing the concept of SW Sex stars (Thorstensenet al. 1991; Hellier 1996).
This object received attention again by the discovery of a nova shell (Sahman et al. 2015, 2018). Using theexpansion velocity, Sahman et al. (2018) suggested that the nova eruption occurred 500–1200 yr ago. Sahmanet al. (2018) could not ﬁnd a corresponding “guest star” in old Chinese and Asian records compiled by Stephenson(1976). Schaefer (2019) could not ﬁnd evidence for a nova eruption in archival plates starting from 1889.
While inspecting of Asteroid Terrestrial-impact Last Alert System (ATLAS: Tonry et al. 2018) forced photometry (Shingles et al. 2021) and Zwicky Transient Facility (ZTF: Masci et al. 2019)1 data, I noticed that thisobject entered a low state starting from early 2023 (vsnet-alert 27760)2 . As far as I know, this is the ﬁrst suchan event since the discovery of this object.
The typical high-state light curve (2016–2019) is shown in ﬁgure 1. The object gradually faded and entereda low state starting from 2023 (ﬁgure 2). Hellier (2000) suggested that SW Sex behavior is caused by episodes ofvery high mass transfer, which are balanced by VY Scl low states (i.e. to adjust to the long-term mass transfer
by angular momentum loss from the binary). In the case of V1315 Aql, the origin of very high mass transfer in
its high state appears to be the result of a nova explosion. The present low state would provide an opportunity
to study the secondary (such as the chemical composition) in detail, which has been hampered by the luminous
accretion disk in the past.
1 The

ZTF data can be obtained from IRSA <https://irsa.ipac.caltech.edu/Missions/ztf.html> using the interface <https://irsa.ipac.caltech.edu/docs/program_interface/ztf_api.html> or using a wrapper of the above IRSA API<https://github.com/MickaelRigault/ztfquery>.
2 <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/27760>.

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Figure 1: Light curve of V1315 Aql in 2016–2019. The object was in high state. Eclipses with depths of 1–2 magwere also present.

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Figure 2: Light curve of V1315 Aql in 2020–2023. The symbols are the same as in ﬁgure 1. The object is in
now low state in 2023 (fourth panel). The bottoms of eclipses in the low state were probably too faint to detectby ATLAS.

4Table 1: Classical novae with low states.
ObjectCP Lac
DK LacHR LyrLV VulV1315 Aql

Eruption
1936
1950
1919
1968
before 1889

Low states
2019–2020
2000–2001, 2020–2022
2010 (shallow)
2018, 2020, 2022
2022

References
vsnet-alert 23621
Henden et al. (2001)
Honeycutt et al. (2014)
this work
this work

Several classical novae (not necessarily SW Sex stars) have been known to show low states recently. They
are summarized in table 1. For CP Lac see vsnet-alert 236213 , which was originally detected by Gaia.4 The
2020–2022 low state of DK Lac was detected in the ZTF data. The light curve of LV Vul from the ZTF data isshown in ﬁgure 3. In addition to them, there are also more candidates:• IV Cep (1971): highly variable in the ZTF data. More than 1 mag fading in 2018 December–2019 April,2020 June–August, 2021 September–? (ending not recorded due to the seasonal gap) and 2022 August–September.
• V400 Per (1974): likely low state in early 2022; only three positive ZTF observations.

Acknowledgements
This work was supported by JSPS KAKENHI Grant Number 21K03616. I am grateful to Naoto Kojiguchi for
helping downloading ZTF data.
This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project.
The ATLAS project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G,
80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from thesurvey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889,
and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible
through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast,
the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Instituteof Astrophysics (MAS), Chile.
Based on observations obtained with the Samuel Oschin 48-inch Telescope at the Palomar Observatory as
part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant
No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar
Klein Center at Stockholm University, the University of Maryland, the University of Washington, DeutschesElektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortiumof Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations
are conducted by COO, IPAC, and UW.
The ztfquery code was funded by the European Research Council (ERC) under the European Union’s Horizon
2020 research and innovation programme (grant agreement n◦ 759194 – USNAC, PI: Rigault).

List of objects in this paper
V1315 Aql, V363 Aur, IV Cep, DQ Her, CP Lac, DK Lac, HR Lyr, V400 Per, VY Scl, LX Ser, SW Sex, LV Vul,KPD 1911+1212, SVS 8130

3 D. Denisenko <http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/23621>.
4 <http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia19elx/>.

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Figure 3: Light curve of LV Vul in 2018–2022. Low state (third panel) and high state (fourth panel); transition
between these state in other panels.

6References
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