BT Monocerotis

{{short description|Nova seen in 1939}}

{{Starbox begin

| name=BT Monocerotis }}

{{Starbox image

| image=

{{Location mark

|image=BTMonLocation.png|alt=|width=280

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|caption=Location of BT Monocerotis (circled in red)

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{{Starbox observe

| epoch=J2000

| ra={{RA|06|43|47.242}}

| dec={{DEC|−02|01|13.88}}

| appmag_v=4.5 – 15.8

| constell=Monoceros }}

{{Starbox character

| class=D/G8V

| b-v=

| u-b=

| variable=Eclipsing binary }}

{{Starbox astrometry

| radial_v=

| prop_mo_ra=

| prop_mo_dec=

| parallax=

| p_error=

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| dist_ly=

| dist_pc={{nowrap|1,413 ± 97}}

| absmag_v= }}

{{Starbox detail

| mass=1.04/0.87

| radius=

| luminosity=

| temperature=

| metal=

| rotation=

| rotational_velocity=—/138

| gravity=

| age= }}

{{Starbox catalog

| names=BT Mon, Nova Monocerotis 1939, 2MASS J06434723-0201139, AAVSO 0638-01, Gaia DR2 3106991818813980416 }}

{{Starbox reference

| Simbad = BT+Mon }}

{{Starbox end}}

BT Monocerotis (Nova Monocerotis 1939) was a nova, which lit up in the constellation Monoceros in 1939. It was discovered on a spectral plate by Fred L. Whipple on December 23, 1939. BT Monocerotis is believed to have reached mag 4.5, which would have made it visible to the naked eye, but that value is an extrapolation; the nova was not observed at peak brightness Its brightness decreased after the outbreak by 3 magnitudes in 182 days, making it a "slow nova". The light curve for the eruption had a long plateau period.

File:BTMonLightCurve.pngs for BT Monocerotis. The main plot, adapted from Schaefer and Patterson (1983), shows the decline from the 1939 nova eruption, and the inset plot, from TESS data, shows the post-eruption brightness fluctuations during an orbital period.]]

Photographic plates taken for 30 years prior to the eruption show that BT Monocerotis remained visible during that period. Prior to 1933, BT Monocerotis had an average magnitude of 15.52 with a variation of 1.2 magnitudes. It retained the same magnitude until the eruption, showing a variation of 0.9 magnitudes. Thus it did not show a pre-eruption rise in brightness.{{cite journal

| author=Collazzi, Andrew C. | title=The Behavior of Novae Light Curves Before Eruption

| journal=The Astronomical Journal | volume=138

| issue=6 | pages=1846–1873 |date=December 2009

| doi=10.1088/0004-6256/138/6/1846

| bibcode=2009AJ....138.1846C |arxiv = 0909.4289 | s2cid=14597316

|display-authors=etal}}

This is an interacting binary star system consisting of a 1.04±0.06{{solar mass|link=y}} white dwarf primary star and a 0.87±0.06{{solar mass}} main sequence star with a stellar classification of G8V. The orbit has a period of 0.33381379 days and an inclination of 88.2° to the line of sight to the Earth, resulting in an eclipsing binary.{{cite conference

|author1=Smith, D. A. |author2=Dhillon, V. S. |author3=Marsh, T. R. | title=The mass of the white dwarf in the old nova BT MON

| book-title=Wild Stars In The Old West: Proceedings of the 13th North American Workshop on Cataclysmic Variables and Related Objects

| series=ASP Conference Series | volume=137 | year=1998

|editor=S. Howell |editor2=E. Kuulkers |editor3=C. Woodward

| page=477 | bibcode=1998ASPC..137..477S }} The nova eruption is believed to have been driven by mass transferred from the secondary star to the white dwarf.{{cite journal

| last=Knigge | first=Christian |date=December 2006

| title=The donor stars of cataclysmic variables

| journal=Monthly Notices of the Royal Astronomical Society

| volume=373 | issue=2| pages=484–502

| doi=10.1111/j.1365-2966.2006.11096.x

| doi-access=free | bibcode=2006MNRAS.373..484K |arxiv = astro-ph/0609671 | s2cid=2616606 }} It remains uncertain whether the white dwarf has an accretion disk formed by this material. Matter outflowing from the system has a line of sight velocity of 450 km s⁻¹, but may be moving at up to 3,200 km s⁻¹ if the flow is strictly bipolar.{{cite journal

|author1=Kafka, S. |author2=Honeycutt, R. K. | title=Detecting Outflows from Cataclysmic Variables in the Optical

| journal=The Astronomical Journal | volume=128 | issue=5

| pages=2420–2429 |date=November 2004

| doi=10.1086/424618 | bibcode=2004AJ....128.2420K | doi-access=free }}