Giant Nemesis candidate HD 107914 / HIP 60503 for the perforation of Oort cloud
aa r X i v : . [ a s t r o - ph . S R ] M a r Giant Nemesis candidate HD 107914 / HIP 60503for the perforation of Oort cloud
Igor Yu. Potemine ∗ Abstract
So far, GJ 710 is the only known star supposed to pass through out-skirts of the solar system within 1 ly. We have reexamined the SIMBADdatabase for additional stellar candidates (from highest ratios of squaredparallax to total proper motion) and compared them with new HIP2 par-allaxes and known radial velocities. At the moment, the best nomineeis double star HD 107914 in the constellation Centaurus at ≈ . v r ofits radial velocity, unknown to the author, we have calculated limits of | v r | necessary to this star to pass within 1 ly and 1 pc from the Sun inlinear approximation. A very accurate value of its total proper motion isalso extremely important. In the case of v r = −
100 km/s and most “ad-vantageous” HIP2 data, HD 107914 could pass as near as 8380 AU fromthe Sun in an almost direct collision course with the inner part of thesolar system! Inversely, if v r had a great positive value, then HIP 60503could be the creator of peculiar trajectories of detached trans-Neptunianobjects like Sedna. Many authors ( cf. [1–4]) have searched past and future stellar perturbersof the Oort cloud. Indeed, it turns out that a massive star passing within 1ly would have a significant influence on long-period comets. More closely,at 10000 AU, such a star would have a serious direct influence on trans-Neptunian objects.Recently, Bobylev [1] has updated the list of stars supposed to transitwithin 2 pc from the Sun using new HIP2 parallaxes. HD 107914 is beyondthe current scope of 30 pc in Bobylev’s studies. This star has two currentlyknown components CCDM J12242-3855AB of visual magnitudes 7.0 and12.8 resp. CCDM attributes the spectral type A5 to the A-component ∗ Universit´e Paul Sabatier, Institut de Math´ematiques de Toulouse (IMT), 118 route deNarbonne, F-31062 Toulouse Cedex 9, France, [email protected] hile SIMBAD considers the double star as an A7/8 giant. [For the sakeof comparison, A5-giant NSV 8327 at ≈ V mag = 6 . V mag = 14 . M ⊙ . We use Julian years and light-years so that 1 parsec = p ≈ . c − ly/y where c ≈ . X be a star with parallax π X (in mas) at the current distance of d X = p · /π X ly from the Sun denoted by the symbol ⊙ . The minimaldistance d min ⊙ X from X to ⊙ is equal to the radius R of the sphere centeredat the Sun and tangent to the trajectory of X . It is easy to show that (cid:12)(cid:12)(cid:12)(cid:12) v r v t (cid:12)(cid:12)(cid:12)(cid:12) = s(cid:18) d X R (cid:19) − v r and v t are radial and transverse velocities of a star X respectively.The transverse velocity can be easily calculated from available cataloguevalues : v t = πc · µ T d X km/s (2)where µ T is the total proper motion of X in mas and π · the numberof radians in 1 mas. From these two formulas we obtain d min ⊙ X = d X √ K + 1 where K = v r v t = 648 · πc × v r µ T d X . (3)Supposing that | v r | = 100 km/s and R π X µ T ' πcp ≈ . π X /µ T ratio and π X /µ T & . π X = 51 . µ α cos( δ ) = 1 . µ δ = 1 .
99 and v r = − . π X /µ T ≈ d min ⊙ X ≈ .
985 ly in a good agreement with known predictions [1, 4].
Limit radial velocities | v lim r, | and | v lim r,p | for stellar transits within 1 ly and1 pc can be obtained from formula (1) with R = 1 and R = p resp. HIP2attributes π X = 12 . ± .
46 and proper motions µ α cos( δ ) = 0 . ± . δ = − . ± . π X = 12 . ± . µ α cos( δ ) = − . ± .
66 and µ δ = 0 . ± .
52 .] Note that proper motions seem to swing around zeroin different prediction modes. We summarize results in table 1 taking intoaccount HIP2 values and measurement errors.
Table 1: Worst, main and best predictions for limit radial velocitiesnecessary for HIP 60503 to pass within 1 ly and 1 pc using HIP2data. π X d X µ T π X /µ T v t | v lim r, | | v lim r,p | (mas) (ly) (mas/yr) (mas × yr) (km/s) (km/s) (km/s)12.31 264.95 1.0024 151.17 0.3860 102.28 31.36 | v r | = 100 km/s, we would get d min ⊙ X ≈ . ≈ Nearby stars with very small proper motions are the best targets in thesearch of potential Nemeses. Our example shows that very accurate mea-surements of proper motions are indispensable for such stars. Then onecan easily create a more or less full list of Nemesis candidates only fromparallaxes and proper motions and calculate limit radial velocities. Fi-nally, eliminating stars with small radial velocities, one can use elaboratedmodels of the galactic potential ( cf. [4]) to calculate stellar trajectories andminimal distances from target stars to the Sun.
References [1] V. Bobylev. Searching for stars closely encountering with the solarsystem.
Astronomy Letters , 36(3), 2010.[2] P. Dybczy´nski. Simulating observable comets III. Real stellar per-turbers of the Oort cloud and their output.
A&A , 446:1233–1242,2006.[3] J. Garc´ıa-S´anchez et al. Stellar encounters with the Oort cloud basedon Hipparcos data. AJ , 117:1042–1045, 1999.[4] J. Garc´ıa-S´anchez et al. Stellar encounters with the solar system. A&A , 379:634–659, 2001.[5] G. Gontcharov. Pulkovo compilation of radial velocities for 35495Hipparcos stars. AL , 32(11):759–771, 2006. cf. catalogue III/252 atSIMBAD.[6] F. van Leeuwen. Validation of the new Hipparcos reduction. A&A ,474:653–664, 2007. cf. catalogue I/311 at SIMBAD.catalogue I/311 at SIMBAD.