The UBV color evolution of classical novae. I. Nova-giant sequence in the color-color diagram

Izumi Hachisu, Mariko Kato

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

We identified a general course of classical nova outbursts in the B-V versus U-B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the main-sequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and near-maximum phases, which we call "the nova-giant sequence." This sequence is parallel to but Δ(U-B) -0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (10-4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B-V = -0.03, U-B = -0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B-V but almost constant in U-B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the color-color diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.

Original languageEnglish
Article number97
JournalAstrophysical Journal
Volume785
Issue number2
DOIs
Publication statusPublished - 2014 Apr 20

Fingerprint

color-color diagram
novae
diagram
color
outburst
intersections
light curve
extinction
envelopes

Keywords

  • cataclysmic variables
  • novae
  • stars: individual (FH Ser, PU Vul, PW Vul, V1500 Cyg, V723 Cas)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The UBV color evolution of classical novae. I. Nova-giant sequence in the color-color diagram. / Hachisu, Izumi; Kato, Mariko.

In: Astrophysical Journal, Vol. 785, No. 2, 97, 20.04.2014.

Research output: Contribution to journalArticle

@article{4f6da7dd1c034365b9e02f32e99c0057,
title = "The UBV color evolution of classical novae. I. Nova-giant sequence in the color-color diagram",
abstract = "We identified a general course of classical nova outbursts in the B-V versus U-B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the main-sequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and near-maximum phases, which we call {"}the nova-giant sequence.{"} This sequence is parallel to but Δ(U-B) -0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (10-4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B-V = -0.03, U-B = -0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B-V but almost constant in U-B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the color-color diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.",
keywords = "cataclysmic variables, novae, stars: individual (FH Ser, PU Vul, PW Vul, V1500 Cyg, V723 Cas)",
author = "Izumi Hachisu and Mariko Kato",
year = "2014",
month = "4",
day = "20",
doi = "10.1088/0004-637X/785/2/97",
language = "English",
volume = "785",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

TY - JOUR

T1 - The UBV color evolution of classical novae. I. Nova-giant sequence in the color-color diagram

AU - Hachisu, Izumi

AU - Kato, Mariko

PY - 2014/4/20

Y1 - 2014/4/20

N2 - We identified a general course of classical nova outbursts in the B-V versus U-B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the main-sequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and near-maximum phases, which we call "the nova-giant sequence." This sequence is parallel to but Δ(U-B) -0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (10-4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B-V = -0.03, U-B = -0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B-V but almost constant in U-B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the color-color diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.

AB - We identified a general course of classical nova outbursts in the B-V versus U-B color-color diagram. It is reported that novae show spectra similar to those of A-F supergiants near optical light maximum. However, they do not follow the supergiant sequence in the color-color diagram, neither the blackbody nor the main-sequence sequence. Instead, we found that novae evolve along a new sequence in the pre-maximum and near-maximum phases, which we call "the nova-giant sequence." This sequence is parallel to but Δ(U-B) -0.2 mag bluer than the supergiant sequence. This is because the mass of a nova envelope is much (10-4 times) less than that of a normal supergiant. After optical maximum, its color quickly evolves back blueward along the same nova-giant sequence and reaches the point of free-free emission (B-V = -0.03, U-B = -0.97), which coincides with the intersection of the blackbody sequence and the nova-giant sequence, and remains there for a while. Then the color evolves leftward (blueward in B-V but almost constant in U-B), owing mainly to the development of strong emission lines. This is the general course of nova outbursts in the color-color diagram, which was deduced from eight well-observed novae in various speed classes. For a nova with unknown extinction, we can determine a reliable value of the color excess by matching the observed track of the target nova with this general course. This is a new and convenient method for obtaining the color excesses of classical novae. Using this method, we redetermined the color excesses of 20 well-observed novae. The obtained color excesses are in reasonable agreement with the previous results, which in turn support the idea of our general track of nova outbursts. Additionally, we estimated the absolute V magnitudes of about 30 novae using a method for time-stretching nova light curves to analyze the distance-reddening relations of the novae.

KW - cataclysmic variables

KW - novae

KW - stars: individual (FH Ser, PU Vul, PW Vul, V1500 Cyg, V723 Cas)

UR - http://www.scopus.com/inward/record.url?scp=84898040239&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84898040239&partnerID=8YFLogxK

U2 - 10.1088/0004-637X/785/2/97

DO - 10.1088/0004-637X/785/2/97

M3 - Article

VL - 785

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 97

ER -