skip to main content


This content will become publicly available on January 1, 2025

Title: A 1.9 solar-mass neutron star candidate in a 2-year orbit

We report discovery and characterization of a main-sequence G star orbiting a dark object with mass1.90±0.04M. The system was discovered via Gaia astrometry and has an orbital period of 731 days. We obtained multi-epoch RV follow-up over a period of 639 days, allowing us to refine the Gaia orbital solution and precisely constrain the masses of both components. The luminous star is a12,Gyr-old, low-metallicity halo star near the main-sequence turnoff (,K; ; ;M0.79M) with a highly enhanced lithium abundance. The RV mass function sets a minimum companion mass for an edge-on orbit ofM2>1.67M, well above the Chandrasekhar limit. The Gaia inclination constraint,i=68.7±1.4,deg, then implies a companion mass ofM2=1.90±0.04M. The companion is most likely a massive neutron star: the only viable alternative is two massive white dwarfs in a close binary, but this scenario is disfavored on evolutionary grounds. The system’s low eccentricity (e=0.122±0.002) disfavors dynamical formation channels and implies that the neutron star likely formed with little mass loss (1M) and with a weak natal kick (). Stronger kicks with more mass loss are not fully ruled out but would imply that a larger population of similar systems with higher eccentricities should exist. The current orbit is too small to have accommodated the neutron star progenitor as a red supergiant or super-AGB star. The simplest formation scenario – isolated binary evolution – requires the system to have survived unstable mass transfer and common envelope evolution with a donor-to-accretor mass ratio>10. The system, which we call Gaia NS1, is likely a progenitor of symbiotic X-ray binaries and long-period millisecond pulsars. Its discovery challenges binary evolution models and bodes well for Gaia’s census of compact objects in wide binaries.

 
more » « less
Award ID(s):
2307232
NSF-PAR ID:
10504055
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
Maynooth Academic Publishing
Date Published:
Journal Name:
The Open Journal of Astrophysics
Volume:
7
ISSN:
2565-6120
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We present high-precision radial velocity observations of Gaia BH1, the nearest known black hole (BH). The system contains a solar-type G star orbiting a massive dark companion, which could be either a single BH or an inner BH + BH binary. A BH + BH binary is expected in some models where Gaia BH1 formed as a hierarchical triple, which is attractive because they avoid many of the difficulties associated with forming the system through isolated binary evolution. Our observations test the inner binary scenario. We have measured 115 precise RVs of the G star, including 40 from ESPRESSO with a precision of 3–5 m s−1, and 75 from other instruments with a typical precision of 30–100 m s−1. Our observations span 2.33 orbits of the G star and are concentrated near a periastron passage, when perturbations due to an inner binary would be largest. The RVs are well-fit by a Keplerian two-body orbit and show no convincing evidence of an inner binary. UsingREBOUNDsimulations of hierarchical triples with a range of inner periods, mass ratios, eccentricities, and orientations, we show that plausible inner binaries with periodsPinner≳ 1.5 days would have produced larger deviations from a Keplerian orbit than observed. Binaries withPinner≲ 1.5 days are consistent with the data, but these would merge within a Hubble time and would thus imply fine-tuning. We present updated parameters of Gaia BH1's orbit. The RVs yield a spectroscopic mass functionfMBH=3.9358±0.0002M—about 7000σabove the ∼2.5Mmaximum neutron star mass. Including the inclination constraint from Gaia astrometry, this implies a BH mass ofMBH= 9.27 ± 0.10M.

     
    more » « less
  2. Abstract

    Many core-collapse supernovae (SNe) with hydrogen-poor and low-mass ejecta, such as ultra-stripped SNe and type Ibn SNe, are observed to interact with dense circumstellar material (CSM). These events likely arise from the core collapse of helium stars that have been heavily stripped by a binary companion and have ejected significant mass during the last weeks to years of their lives. In helium star models run to days before core collapse we identify a range of helium core masses ≈2.5–3Mwhose envelopes expand substantially due to the helium shell burning while the core undergoes neon and oxygen burning. When modeled in binary systems, the rapid expansion of these helium stars induces extremely high rates of late-stage mass transfer (Ṁ102Myr1) beginning weeks to decades before core collapse. We consider two scenarios for producing CSM in these systems: either mass transfer remains stable and mass loss is driven from the system in the vicinity of the accreting companion, or mass transfer becomes unstable and causes a common envelope event (CEE) through which the helium envelope is unbound. The ensuing CSM properties are consistent with the CSM masses (∼10−2–1M) and radii (∼1013–1016cm) inferred for ultra-stripped SNe and several type Ibn SNe. Furthermore, systems that undergo a CEE could produce short-period neutron star binaries that merge in less than 100 Myr.

     
    more » « less
  3. Abstract

    The warm Neptune GJ 3470b transits a nearby (d= 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity ofλ=9812+15and avsini=0.850.33+0.27kms1. Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity ofψ=958+9, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope ofγ̇=0.0022±0.0011ms1day1over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere.

     
    more » « less
  4. Abstract

    M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similarTeff∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution (R∼ 35,000)K-band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and findMB=88.03.2+3.4MJup, putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star witha=383+4au ande= 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect13CO (7.8σsignificance) and tentatively detectH218O(3.7σsignificance) in the companion’s atmosphere and measure12CO/13CO=9822+28andH216O/H218O=24080+145after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure12CO/13CO=7916+21andC16O/C18O=28870+125for the primary star. These results demonstrate that HIP 55507 A and B have consistent12C/13C and16O/18O to the <1σlevel, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring13CO andH218Oabundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types.

     
    more » « less
  5. Abstract

    We present and confirm TOI-1751 b, a transiting sub-Neptune orbiting a slightly evolved, solar-type, metal-poor star (Teff= 5996 ± 110 K,log(g)=4.2±0.1,V= 9.3 mag, [Fe/H] = −0.40 ± 0.06 dex) every 37.47 days. We use TESS photometry to measure a planet radius of2.770.07+0.15R. We also use both Keck/HIRES and APF/Levy radial velocities (RV) to derive a planet mass of14.53.14+3.15M, and thus a planet density of 3.6 ± 0.9 g cm−3. There is also a long-period (∼400 days) signal that is observed in only the Keck/HIRES data. We conclude that this long-period signal is not planetary in nature and is likely due to the window function of the Keck/HIRES observations. This highlights the role of complementary observations from multiple observatories to identify and exclude aliases in RV data. Finally, we investigate the potential compositions of this planet, including rocky and water-rich solutions, as well as theoretical irradiated ocean models. TOI-1751 b is a warm sub-Neptune with an equilibrium temperature of ∼820 K. As TOI-1751 is a metal-poor star, TOI-1751 b may have formed in a water-enriched formation environment. We thus favor a volatile-rich interior composition for this planet.

     
    more » « less