J/A+A/631/A48 rho Cas differential BVRI photometry (van Genderen+, 2019)
Pulsations, eruptions and evolution of four yellow hypergiants. I.
van Genderen A.M., Lobel A., Nieuwenhuijzen H., Henry G.W., de Jager C.,
Blown E., Di Scala G., van Ballegoij E.J.
<Astron. Astrophys. 631, A48 (2019)>
=2019A&A...631A..48V 2019A&A...631A..48V (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, luminous ; Interstellar medium ;
HR diagrams ; Photometry, UBVRI
Keywords: stars: massive - supergiants - stars: oscillations -
technique: photometric
Abstract:
We aim to explore the variable photometric and stellar properties of
four yellow hypergiants (YHGs), HR 8752, HR 5171A, rho Cas, and HD
179821, and their pulsations of hundreds of days, and long-term
variations (LTVs) of years. We also aim to explore light and colour
curves for characteristics betraying evolutionary loops and eruptive
episodes and to investigate trends of quasi-periods and the possible
need for distance revisions. We tackled multi-colour and visual
photometric data sets, looked for photometric indications betraying
eruptions or enhanced mass-loss episodes, calculated stellar
properties mainly using a previously published temperature
calibration, and investigated the nature of LTVs and their influence
on quasi-periods and stellar properties. Based on driven one-zone
stellar oscillation models, the pulsations can be characterised as
'weakly chaotic'.
The BV photometry revealed a high-opacity layer in the atmospheres.
When the temperature rises the mass loss increases as well,
consequently, as the density of the high-opacity layer. As a result,
the absorption in B and V grow. The absorption in B, presumably of the
order of one to a few 0.1mag, is always higher than in V. This
difference renders redder and variable (B-V) colour indexes, but the
absorption law is unknown. This property of YHGs is unpredictable and
explains why spectroscopic temperatures (reddening independent) are
always higher than photometric ones, but the difference decreases with
the temperature. A new (weak) eruption of rho Cas has been identified.
We propose shorter distances for rho Cas and HR 5171A than the
accepted ones. Therefore, a correction to decrease the blue
luminescence of HR 5171A by polycyclic aromatic hydrocarbon (PAH)
molecules is necessary, and HR 5171A would no longer be a member of
the cluster Gum48d. HR 5171A is only subject to one source of light
variation, not by two as the literature suggests. Eruptive episodes
(lasting one to two years), of YHGs prefer relatively cool
circumstances when a red evolutionary loop (RL) has shifted the star
to the red on the HR diagram. After the eruption, a blue loop
evolution (BL) is triggered lasting one to a few decades. We claim
that in addition to HR 8752, also the other three YHGs have shown
similar cycles over the last 70 years. This supports the suspicion
that HD 179821 might be a YHG (with a possible eruptive episode
between 1925 and 1960). The range in temperature of these cyclic Teff
variations is 3000K-4000K. LTVs mainly consist of such BL and RL
evolutions, which are responsible for a decrease and increase,
respectively, of the quasi-periods. The reddening episode of HR 5171A
between 1960 and 1974 was most likely due to a red loop evolution, and
the reddening after the 1975 eruption was likely due to a shell
ejection, taking place simultaneously with a blue loop evolution.
Description:
Tablem1 contains the full T2 APT VRI photometric dataset of rho Cas,
1986-2001. Magnitudes (mag) of variable (Var) and check (Chk) star are
relative to the comparison star HD 223173.
Tablem2 contains the full T3 APT BV photometric dataset of rho Cas,
2003-2018.
Objects:
--------------------------------------------
RA (2000) DE Designation(s)
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23 54 23.03 +57 29 57.8 rho Cas = HR 9045
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablem1.dat 52 1772 VRI Photometric Observations of rho Cas from T2 APT
tablem2.dat 38 1351 BV Photometric Observations of rho Cas from T3 APT
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Byte-by-byte Description of file: tablem1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d HJD Heliocentric Julian Date (HJD-2400000)
12- 17 F6.3 mag VarV ?=99.999 Variable - Comparison differential
magnitude in V (1)
19- 24 F6.3 mag VarR ?=99.999 Variable - Comparison differential
magnitude in R (1)
26- 31 F6.3 mag VarI ?=99.999 Variable - Comparison differential
magnitude in I (1)
33- 38 F6.3 mag ChkV ?=99.999 Check - Comparison differential
magnitude in V (1)
40- 45 F6.3 mag ChkR ?=99.999 Check - Comparison differential
magnitude in V (1)
47- 52 F6.3 mag ChkI ?=99.999 Check - Comparison differential
magnitude in V (1)
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Note (1): The '99.999' signifies that the differential magnitude was discarded
because its internal standard deviation exceeded 0.02mag.
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Byte-by-byte Description of file: tablem2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.4 d HJD Heliocentric Julian Date (HJD-2400000)
12- 17 F6.3 mag VarB ?=99.999 Variable - Comparison differential
magnitude in B (1)
19- 24 F6.3 mag VarV ?=99.999 Variable - Comparison differential
magnitude in V (1)
26- 31 F6.3 mag ChkB ?=99.999 Check - Comparison differential
magnitude in B (1)
33- 38 F6.3 mag ChkV ?=99.999 Check - Comparison differential
magnitude in V (1)
--------------------------------------------------------------------------------
Note (1): The '99.999' signifies that the differential magnitude was discarded
because its internal standard deviation exceeded 0.01mag.
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Acknowledgements:
Alex Lobel, Alex.Lobel(at)oma.be
(End) Alex Lobel [ROB, Belgium], Patricia Vannier [CDS] 24-Sep-2019