J/AJ/158/175 Photometric & spectroscopic study of AF And in M31 (Joshi+, 2019)
A long-term photometric variability and spectroscopic study of luminous blue
variable AF And in M31.
Joshi Y.C., Sharma K., Gangopadhyay A., Gokhale R., Misra K.
<Astron. J., 158, 175 (2019)>
=2019AJ....158..175J 2019AJ....158..175J (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, supergiant ; Stars, blue ;
Stars, variable ; Photometry, RI ; Spectroscopy
Keywords: galaxies: individual (M31) - methods: observational - stars: massive -
stars: winds, outflows - techniques: photometric -
techniques: spectroscopic
Abstract:
We present a photometric and spectroscopic analysis of the Hubble-Sandage
variable star AF And in M31. The data have been taken under the Nainital
Microlensing Survey during 1998-2002, and follow-up observations were
carried out until 2011. During this period, photometric observations
in Cousins R and I bands were obtained for 169 nights spanning about
5000 days. AF And showed a prominent outburst around 1999 mid-January,
followed by a gradual decrease in brightness of about 1.5 mag in the next
3 yr with a declining rate of ∼0.0015 mag/day, leading to a quiescent
phase at the end of 2001. After lying low for about 9 yr, AF And again
went through a secondary outburst phase in late 2010 with an amplitude
of 0.44 mag, where it lasted for one year before fading back to its
quiescent phase. Spectroscopic observations of AF And show prominent
Balmer and He I emission lines along with the comparatively weaker Fe II
and [Fe II] emissions. Asymmetric emission line profiles in its spectrum
imply a mass-loss rate of about 2.2x10-4 M☉/yr through the stellar
winds in the photosphere. Using spectral energy distribution fitting,
we find a photospheric temperature of 33000±3000 K during the visual
minimum. Using a weak P Cygni profile of the He I emission line, the wind
terminal velocity for AF And is found to be around 280-300 km/s.
Description:
Table 2 contains the flux calibrated spectrum of of the Hubble-Sandage
variable star AF And in M31, and Table 1 the observing log. The Cousins
R- and I-band photometric data of AF And were acquired on 169 nights
spanning a duration of about 5000 days. In total more than 1300 frames
in the R and I bands were collected, using two different telescopes,
the 1.04 m Sampurnanand Telescope (ST) at Manora Peak, Nainital, India
and the 2 m Himalayan Chandra Telescope (HCT). The spectroscopic
observations were carried out using the Hanle Faint Object Spectrograph
Camera (HFOSC) mounted on 2.0 m HCT, operated by the Indian Institute
of Astrophysics (IIA) at Hanle, Ladakh, India, in low-resolution mode
on the night of 2016 September 10. We used an SITe CCD of 2Kx4K pixels
with pixel size of 15µx15µ and image scale of 0.29"/pixel. We used
grism gr7 (3800-6800 Å) and a slit width of 0.77" (67 µ), giving a
spectral resolution of R∼1300. The far visible region of the spectrum
was collected using gr8 (5800-8400 Å) with a slit width of 1.15"
(100 µ) and a resolution of R∼2200.
Objects:
-----------------------------------------------------
RA (ICRS) DE Designation(s)
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00 42 44.33 +41 16 07.5 M31 = NAME Andromeda
00 43 33.09 +41 12 10.3 AF And = BASW 19
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 169 Observing log of the data
table2.dat 40 169 The R and I magnitudes of the star AF And and
their corresponding errors in each of the
observed nights
fig4gr7.dat 16 2777 Flux calibrated gr7 spectrum of AF And as shown
in Figure 4
fig4gr8.dat 16 2707 Flux calibrated gr8 spectrum of AF And as shown
in Figure 4
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See also:
J/A+A/402/113 : (RI)c photometry of variables in M31 (Joshi+, 2003)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/ApJ/790/48 : Variable stars in M31 & M33. II. LBVs (Humphreys+, 2014)
J/AJ/152/62 : Revised LGGS UBVRI of M31 and M33 stars (Massey+, 2016)
J/ApJ/825/50 : Variable stars in M31 & M33. III. (Gordon+, 2016)
J/AJ/154/81 : BVRI photometry of luminous stars in M31 and M33
(Martin+, 2017)
J/ApJ/836/64 : Luminous variable stars in M31 & M33. IV. (Humphreys+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "date" Date Observation date
12- 24 F13.5 d mJD Mid-Julian Day of observation
26- 29 F4.2 arcsec FWHM [0.71/3.32] PSF Full-Width at Half-Maximum
31- 32 I2 --- NR [1/47]? Number of R band frames
34- 37 I4 s ExpR [60/1200]? Exposure time in R band
39- 40 I2 --- NI [1/30]? Number of I band frames
42- 45 I4 s ExpI [60/1200]? Exposure time in I band
47- 49 A3 --- Tel Telescope code (ST or HCT)
51- 55 A5 --- CCD CCD used
57- 63 A7 arcmin FoV Field of View
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- IDobs [1/169] Observation serial number
5- 14 F10.5 d mJD Mid-Julian Day of observation (JD-2450000)
16- 21 F6.3 mag Rmag [15.896/17.343]? Apparent Cousins R band magnitude
23- 27 F5.3 mag e_Rmag [0.003/0.083]? Uncertainty in Rmag
29- 34 F6.3 mag Imag [15.794/17.3]? Apparent Cousins I band magnitude
36- 40 F5.3 mag e_Imag [0.003/0.06]? Uncertainty in Imag
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Byte-by-byte Description of file: fig4gr7.dat fig4gr8.dat
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Bytes Format Units Label Explanations
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1- 4 I4 0.1nm Wave [3608/8908] Wavelength (Å) (1)
6- 16 E11.6 10-2W/m2/nm Flux [1.51015e-16/7.96979e-15] Flux
(in erg/s/cm2/Å) (1)
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Note (1): The gr7 and gr8 spectra were obtained on mid-Julian days
2457642.29087 and 2457642.32407, respectively.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 11-Dec-2019