C/1913 Y1 Delavan
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Comet C/1913 Y1 was discovered on 18 December 1913 by Paulnbsp;T.nbsp;Delavan (La Plata Observatory, Argentina), that is about ten months before its perihelion passage, and the comet was last seen on 19 September 1915 [Kronk, Cometography: Volume 3].
This comet made its closest approach to the Earth on 4 October 1914 (1.58 au), that is 9.5 months after its discovery.
Solutions given here are based on data spanning over 1.72 yr in a range of heliocentric distances from 4.24 au through perihelion (1.10 au) to 4.26 au.
Pure gravitational orbit determined from all available positional measurements (1006 observations) give 1a-class orbit, orbit given in Minor Planet Center is 1B class (339 obs. used, the same arc of data; see MPC).
It was possible to determine the non-gravitational orbit for C/1913 Y1 (preferred orbit), the decrease of RMS is small (from 2.06 arcsec to 2.00 arcs) though only radial non-gravitational parameter was determined.
This Oort spike comet suffers very slight planetary perturbations during its passage through the planetary system, and in the next passage through the perihelion it will enter the planet zone as Oort spike comet (see future barycentric orbits for both solutions: pure gravitational and non-gravitational).
This comet was in the original sample of 19 comets used by Oort for his hypothesis on LPCs; however, according to presented here statistics for previous perihelion passage its dynamical status is uncertain.
More details in Królikowska et al. 2014.

solution description
number of observations 1006
data interval 1913 12 18 – 1915 09 07
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 4.24 au – 1.10 au (perihelion) – 4.26 au
type of model of motion NS - non-gravitational orbits for standard g(r)
data weighting YES
number of residuals 1860
RMS [arcseconds] 2.00
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1914 11 04
perihelion date 1914 10 26.76701183 ± 0.00006224
perihelion distance [au] 1.10444242 ± 0.00000218
eccentricity 1.00009618 ± 0.00000906
argument of perihelion [°] 97.467000 ± 0.000059
ascending node [°] 60.396112 ± 0.000023
inclination [°] 68.038602 ± 0.000059
recip semi-major axis [10-6 au-1] -87.08 ± 8.20
Time distribution of positional observations with corresponding heliocentric (red curve) and geocentric (green curve) distance at which they were taken. The horizontal dotted line shows the perihelion distance for a given comet whereas vertical dotted line – the moment of perihelion passage
non-gravitational parameters
A1 [10-8au/day2] 1.24 ± 0.172
A2 [10-8au/day2] 0 (assumed)
A3 [10-8au/day2] 0 (assumed)
m -2.15
n 5.093
k -4.6142
r0 [au] 2.808
α 0.1113