No Period Change in Two Long-Period AM CVn Binaries
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| Format: | Preprint |
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2026
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| author | Green, Matthew J. Marsh, Thomas R. van Roestel, Jan Wong, Tin Long Sunny Belloni, Diogo Kilic, Mukremin Breedt, Elme Brown, Alex Copperwheat, Chris M. Chakpor, Anurak Dhillon, V. S. Segura, Noel Castro Dyer, Martin J. Garbutt, James Jarvis, Dan Kengkriangkrai, Vasu Kennedy, Mark R. Kerry, Paul Kupfer, Thomas Littlefair, S. P. McCormac, James Munday, James Parsons, Steven G. Pike, Eleanor Pelisoli, Ingrid Rodriguez-Gil, Pablo Sahman, David I. Yates, Amalie |
| author_facet | Green, Matthew J. Marsh, Thomas R. van Roestel, Jan Wong, Tin Long Sunny Belloni, Diogo Kilic, Mukremin Breedt, Elme Brown, Alex Copperwheat, Chris M. Chakpor, Anurak Dhillon, V. S. Segura, Noel Castro Dyer, Martin J. Garbutt, James Jarvis, Dan Kengkriangkrai, Vasu Kennedy, Mark R. Kerry, Paul Kupfer, Thomas Littlefair, S. P. McCormac, James Munday, James Parsons, Steven G. Pike, Eleanor Pelisoli, Ingrid Rodriguez-Gil, Pablo Sahman, David I. Yates, Amalie |
| contents | Ultracompact binary systems, consisting of two compact objects in an orbit $\lesssim 0.5 R_\odot$, should exhibit measurable rates of orbital period change ($\dot{P} \neq 0$) due to the emission of gravitational waves (GWs). Measurements of \pdot\ have so far been limited to the shortest-period ultracompact binaries ($\lesssim 20$\,min). Among the AM\,CVn-type subclass, several works have proposed the presence of extra angular momentum loss beyond GW emission, with magnetic braking being a widely discussed mechanism. If present, this magnetic braking would dominate the angular momentum loss of AM\,CVn-type binaries with orbital periods $\gtrsim 30$\,min. In this work, we present a long-term eclipse timing study of two AM\,CVn-type binaries, YZ\,LMi and Gaia14aae, with respective orbital periods of 28.3\,min and 49.7\,min and continuous observations since 2006 and 2015. Both systems show $\dot{P}$ consistent with zero within $2σ$. Their $3σ$ upper limits are $1.1 \times 10^{-13}\,{\rm s \, s}^{-1}$ and $9.7 \times 10^{-14}\,{\rm s \, s}^{-1}$ respectively. These non-detections are most simply explained by a scenario in which secular angular momentum loss is not substantially stronger than GW emission at all orbital periods, but is combined with deviations from the secular $\dot{P}$ whose timescales span decades but whose amplitude is $\lesssim 10^{-13}\,{\rm s \, s}^{-1}$. %, orders of magnitude smaller than the eclipse timing variations seen in hydrogen-dominated cataclysmic variables. Our non-detections of $\dot{P}$ represent a limit on the strength of any enhanced angular momentum loss beyond pure GW emission. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_06460 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | No Period Change in Two Long-Period AM CVn Binaries Green, Matthew J. Marsh, Thomas R. van Roestel, Jan Wong, Tin Long Sunny Belloni, Diogo Kilic, Mukremin Breedt, Elme Brown, Alex Copperwheat, Chris M. Chakpor, Anurak Dhillon, V. S. Segura, Noel Castro Dyer, Martin J. Garbutt, James Jarvis, Dan Kengkriangkrai, Vasu Kennedy, Mark R. Kerry, Paul Kupfer, Thomas Littlefair, S. P. McCormac, James Munday, James Parsons, Steven G. Pike, Eleanor Pelisoli, Ingrid Rodriguez-Gil, Pablo Sahman, David I. Yates, Amalie Solar and Stellar Astrophysics Ultracompact binary systems, consisting of two compact objects in an orbit $\lesssim 0.5 R_\odot$, should exhibit measurable rates of orbital period change ($\dot{P} \neq 0$) due to the emission of gravitational waves (GWs). Measurements of \pdot\ have so far been limited to the shortest-period ultracompact binaries ($\lesssim 20$\,min). Among the AM\,CVn-type subclass, several works have proposed the presence of extra angular momentum loss beyond GW emission, with magnetic braking being a widely discussed mechanism. If present, this magnetic braking would dominate the angular momentum loss of AM\,CVn-type binaries with orbital periods $\gtrsim 30$\,min. In this work, we present a long-term eclipse timing study of two AM\,CVn-type binaries, YZ\,LMi and Gaia14aae, with respective orbital periods of 28.3\,min and 49.7\,min and continuous observations since 2006 and 2015. Both systems show $\dot{P}$ consistent with zero within $2σ$. Their $3σ$ upper limits are $1.1 \times 10^{-13}\,{\rm s \, s}^{-1}$ and $9.7 \times 10^{-14}\,{\rm s \, s}^{-1}$ respectively. These non-detections are most simply explained by a scenario in which secular angular momentum loss is not substantially stronger than GW emission at all orbital periods, but is combined with deviations from the secular $\dot{P}$ whose timescales span decades but whose amplitude is $\lesssim 10^{-13}\,{\rm s \, s}^{-1}$. %, orders of magnitude smaller than the eclipse timing variations seen in hydrogen-dominated cataclysmic variables. Our non-detections of $\dot{P}$ represent a limit on the strength of any enhanced angular momentum loss beyond pure GW emission. |
| title | No Period Change in Two Long-Period AM CVn Binaries |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2604.06460 |